In the southern Great Plains, the encroachment of grassland ecosystems by mesquite (Prosopis glandulosa), is widespread, and prescribed fire is commonly used in its control. Despite this, substantial quantitative information concerning their influences on the community composition, functional dynamics, and soil organic carbon (SOC) storage potential of grassland ecosystems is lacking. The objectives of this study were to: a) quantify the effects of seasonal prescribed fire treatments and mesquite encroachment on aboveground net primary productivity (ANPP) and herbaceous community composition; b) characterize SOC pool sizes, turnover, and storage potential relative to vegetation type and fire treatment; c) evaluate the structure and diversity of soil microbial communities relative to vegetation type; and d) characterize the functional diversity of these same microbes using the GeoChip functional gene microarray. Repeated winter and summer fires led to increased ANPP rates (average, 434 and 313 g m-2 y-1, respectively), relative to unburned controls (average, 238 g m-2 y-1), altered herbaceous community composition, and increased the storage of resistant forms of SOC, but did not affect overall SOC storage. Herbaceous ANPP rates did not differ significantly as a result of mesquite encroachment, but herbaceous community composition and SOC storage did. Mesquite soils contained significantly more total, slow-turnover, and resistant forms of SOC than those that occurred beneath C3 or C4 grasses. Similarity among the soil bacterial and fungal communities associated with the major vegetation types in this system was low to moderate. Significant differences were detected among soil fungi, with the mesquite-associated fungi harboring significant differences in community structure relative to the fungal communities associated with each of the other vegetation types examined. Despite this result, few significant differences were detected with respect to the functional diversity of these communities, suggesting either a high degree of functional redundancy, or that the functional differences harbored by these communities are beyond the scope of the GeoChip. The results of this study demonstrate that both fire and mesquite encroachment have the potential to alter ecosystem components and processes significantly, providing new insight regarding the effects of these widespread land use and land cover changes on ecosystem structure and function.

Homeotherms and many poikilotherms display a positive relationship between body size and latitude, but this has rarely been investigated in microscopic animals. We analysed all published records of marine Tardigrada to address whether microscopic marine invertebrates have similar ecogeographical patterns to macroscopic animals. The data were analysed using spatially explicit generalized least squares models and linear models. We looked for latitudinal patterns in body size and species richness, testing for sampling bias and phylogenetic constraints. No latitudinal pattern was detected for species richness, and sampling bias was the strongest correlate of species richness. A hump-shaped increase in median body size with latitude was found, and the effect remained significant for the Northern Hemisphere but not for the Southern. The most significant effect supporting the latitudinal gradient was on minimum body size, with smaller species disappearing at higher latitudes. Our results suggest that biogeographical signals were observed for body size, albeit difficult to detect in poorly studied groups because of swamping from biased sampling effort and from low sample size. We did not find a significant correlation with the latitudinal pattern of body size and ecologically relevant net primary productivity.

This study estimated monthly and annual Net Primary Productivity (NPP), an important indicator of carbon sequestration, in the Conterminous US from 1997 to 2007 using Carnegie-Ames-Stanford Approach. Vegetation condition, temperature, precipitation, photosynthetically active radiation and soil water holding capacity were used as model’s inputs. NPP values were lower than mean annual values during the year 2000 to 2003 which was probably due to extreme drought conditions during these years. Higher NPP per square meter was generally found in Savannah and Subtropical eco-divisions whereas Tropical/Subtropical deserts had the lowest NPP. Southeastern states had the highest NPP per square meter thus, made the highest contribution to the terrestrial carbon sequestration in US. Since the vegetation is one of the main factors in NPP and thus carbon sequestration, the results of this study could help in various environmental policy decisions on forest and cropland management at the state, EPA and federal levels.

Increased nutrient availability globally has the potential to affect community functional composition of plants in nutrient limited environments, such as coastal grassland systems. Stability of these systems are threatened worldwide by urbanization, as well as effects of sea level rise and increased frequency and intensity of storms, and atmospheric N deposition, associated with climate change. Annual net primary productivity (ANPP), species composition, and functional traits (community weighted specific leaf area (CWSLA), leaf area index (LAI), growth form and photosynthetic pathway) were measured across four treatments to assess multiple resource limitation of nitrogen (N) and phosphorus (P) and functional community response in a coastal grassland on Hog Island, VA within the Virginia Coast Reserve, Long Term Ecological Research Network (LTER) applied at a rate of 10 g m-2 yr-1 Nutrient enrichment did not alter species diversity or richness. ANPP was highest in plots receiving any type of nitrogen enrichment, and was higher than expected of low nutrient systems. CWSLA was significantly higher in NP plots, and was lower than other grasslands. P treatments were not significantly different from controls. Graminoid species, specifically C4 species responded with higher ANPP than C3 forbs or graminoids within treatments. Evidence of synergistic NP effects were seen on community level resource allocation and leaf construction, but no significant species changes occurred over a 1-year time span. These results have expanded the knowledge of functional response to increased nutrient availability in an understudied, coastal grassland, which are at high risk to being lost to sea level rise and anthropogenic development and inform community assembly processes in stressful environments.

<p>Since the pre-industrial age, the Earth has been warming at unparalleled rates, and this warming is changing climate and weather, creating a more extreme global hydrological cycle. In this dissertation, I explore how these changes to the hydrological cycle may act ecosystem and community level responses of terrestrial plants in the Midwestern United States. In this region, it is projected that mean annual precipitation (MAP) will increase, but precipitation will become more variable across and within seasons. Ecosystem structure and function are vulnerable to changes in hydrologic patterns, including changes in biogeochemical cycles, plant productivity, and plant community structure and function. In this dissertation, I explore how changes in precipitation will alter these processes using two field experiments, and I suggest potential hypotheses that could explain drought-induced community change.</p><p><br></p><p>In chapter 1, I explore how alterations to seasonal precipitation in the winter and summer act ecosystem and community processes in a temperate deciduous forest. Biogeochemical processes and plant communities are sensitive to changes in abiotic conditions, and these conditions will alter forest succession, particularly juvenile woody plant species. Using a fully factorial experiment, I manipulated winter snowfall and summer precipitation to create wet, dry, and control (ambient conditions) treatments and investigated how changes in seasonal precipitation would act mineralization rates, woody plant recruitment, and understory composition. I found that the effects of winter and summer precipitation on these processes acted independently of one another in this system, and the system was resistant to changes in mineralization rates and understory composition. Woody plant recruitment may be more sensitive to altered precipitation, as recruitment of at least one of the four species planted, Lindera benzoin, was impacted by changes in seasonal precipitation. Snow removal treatments reduced germination and increased summer precipitation decreased the relative growth rate of this species. In the short term, slight changes to woody plant recruitment may have little impact on long-term forest succession, but as these changes persist over longer periods of time, they could alter the direction of succession, which could lead to changes in the understory community composition and nutrient cycling.</p> <p><br></p><p>The second and third chapters explore the effects that drought intensification will have on terrestrial plant communities. Numerous studies have investigated the effects of individual droughts on ecosystem and community responses, but the effects that both the timing and duration of drought have on these responses remain largely unknown. To explore this gap in the literature, I conducted a eld experiment using rainout shelters to reduce growing season precipitation, creating dry periods that varied in length and timing. Drought can impact productivity and diversity in this system, and the timing in which the drought occurs influences these effects. Surprisingly, I found that the length of drought did not affect productivity or community composition.</p> <p><br></p><p>The final chapter introduces the Community Response to Extreme Drought framework CRED), which addresses the potential temporal progression of mechanisms and plant-plant interactions that may lead to community changes during and after a drought. The mechanisms for the temporal evolution of community-level drought responses are not fully understood, but plant-plant interactions, both competitive (-) and facilitative (+), are increasingly being recognized as important drivers of community compositional changes. The CRED framework provides hypotheses for the roles that plant-plant interactions have on drought-induced community change. CRED addresses how system-specific variables and the intensity of drought may influence the strength of plant-plant interactions over time, and ultimately the systems resistance and resilience to drought. </p><p><br></p><p>The results from this dissertation work have revealed that more research needs to be done to fully understand how changes in precipitation regimes and patterns will affect terrestrial ecosystems and plant communities. A better understanding of how ecosystems and communities respond to drought timing and length can help improve climate models and restoration strategies.</p>

Biomass is an important ecological variable for understanding the responses of vegetation to the currently observed global change. The impact of changes in vegetation biomass on the global ecosystem is also of high relevance. The vegetation in the arid and semi-arid environments of Kazakhstan is expected to be affected particularly strongly by future climate change. Therefore, it is of great interest to observe large-scale vegetation dynamics and biomass distribution in Kazakhstan. At the beginning of this dissertation, previous research activities and remote-sensing-based methods for biomass estimation in semi-arid regions have been comprehensively reviewed for the first time. The review revealed that the biggest challenge is the transferability of methods in time and space. Empirical approaches, which are predominantly applied, proved to be hardly transferable. Remote-sensing-based Net Primary Productivity (NPP) models, on the other hand, allow for regional to continental modelling of NPP time-series and are potentially transferable to new regions. This thesis thus deals with modelling and analysis of NPP time-series for Kazakhstan and presents a methodological concept for derivation of above-ground biomass estimates based on NPP data. For validation of the results, biomass field data were collected in three study areas in Kazakhstan. For the selection of an appropriate model, two remote-sensing-based NPP models were applied to a study area in Central Kazakhstan. The first is the Regional Biomass Model (RBM). The second is the Biosphere Energy Transfer Hydrology Model (BETHY/DLR). Both models were applied to Kazakhstan for the first time in this dissertation. Differences in the modelling approaches, intermediate products, and calculated NPP, as well as their temporal characteristics were analysed and discussed. The model BETHY/DLR was then used to calculate NPP for Kazakhstan for 2003–2011. The results were analysed regarding spatial, intra-annual, and inter-annual variations. In addition, the correlation between NPP and meteorological parameters was analysed. In the last part of this dissertation, a methodological concept for derivation of above-ground biomass estimates of natural vegetation from NPP time-series has been developed. The concept is based on the NPP time-series, information about fractional cover of herbaceous and woody vegetation, and plants’ relative growth rates (RGRs). It has been the first time that these parameters are combined for biomass estimation in semi-arid regions. The developed approach was finally applied to estimate biomass for the three study areas in Kazakhstan and validated with field data. The results of this dissertation provide information about the vegetation dynamics in Kazakhstan for 2003–2011. This is valuable information for a sustainable land management and the identification of regions that are potentially affected by a changing climate. Furthermore, a methodological concept for the estimation of biomass based on NPP time-series is presented. The developed method is potentially transferable. Providing that the required information regarding vegetation distribution and fractional cover is available, the method will allow for repeated and large-area biomass estimation for natural vegetation in Kazakhstan and other semi-arid environments.

No description available.

<p>Earth’s ecosystems emerge from interconnected biosphere, geosphere, and atmosphere processes. Changes to any one process ripple through the Earth system, affecting other processes. As global climate change continues, nitrogen deposition is anticipated to increase and precipitation is expected to have varied changes across the globe. These changes to the atmosphere and geosphere will have implications for the biosphere. Namely, vegetation will be impacted by changes to nutrient and precipitation regimes. Vegetation comprises the aggregate strategies of individual plants, which are also influenced by changes in nutrient and water availability. The responses of individual plants to nitrogen, water, and uncertainty are the main focus of this dissertation, as understanding those will be critical to scaling up to the aggregate.</p> <p> First, I describe a mathematical model that predicts grassland root and shoot biomass across carbon, nitrogen, and water gradients. The model simulates competition among plants by dynamically allocating carbon to either root or shoot growth depending on the growth strategy employed by the other plant. I show that the model accurately predicts root net primary productivity (NPP), but performs poorly for shoot and total NPP. At the biome scale, modeled NPP does not vary with water alone but rather water and nitrogen interact to influence NPP. Second, I conduct a greenhouse experiment using <em>Eragrostis capillaris</em> (L.) Nees to examine the predictions of the model mentioned above to answer the question: how do water and nitrogen affect fitness and biomass allocation in a drought-tolerant C4 grass? And ask: what is the nature of the relationship between water and nitrogen as resources? I show that water was important for increasing shoot and total biomass, but that root biomass and root:shoot ratio was influenced interactively by water and nitrogen as predicted by the model. I conclude that the nature of the relationship between water and nitrogen was that of either interacting or hemi-essential resources. That is, additional water was able to partially substitute for limited nitrogen to maintain biomass. Third, I explore how information theory can apply to plants that face uncertainty in resource availability and briefly review the types and sources of information and the mechanisms that plants use to perceive and respond to their environment. Overall, my framework posits that plants interpret information from their surroundings as an emergent property of distributed information processed by a network of cells. I end with a prospectus of directions for future research, including decoding signal from noise, storage of information, strategies to cope with information entropy, additional means of information transmission, and two-way information signaling with biotic partners. Finally, I use the information theory framework discussed above to answer the questions: can plants sense and respond to information entropy? I explore this question using data from an experiment which altered the temporal supply of nutrients and found no support that <em>P. sativum</em> can sense and respond to entropy. Understanding the relationships of water, nitrogen, and uncertainty is critical to predicting plant growth, especially as climate change continues to influence the global system.</p>

自工業革命後，隨著科技的進步，人口、經濟、醫療技術皆快速發展，也因人類需求的增加而大量燃燒化石燃料，大規模的砍伐熱帶雨林，導致大氣中二氧化碳大量增加，進而衍生溫室效應的發生，甚至造成全球氣候變遷。 在全球暖化的狀態下，聯合國氣候變化綱要公約與京都議定書中都明確肯定森林可固定主要溫室氣體二氧化碳，由於森林具備吸收和儲存二氧化碳的能力，其對於生態系統中的碳循環功能扮演重要的角色。若能有效監控森林資源，便能管理溫室氣體，且能提出有效的控管方式。 而本研究將應用遙測技術於碳吸存與環境變化的監測，透過美國大地衛星影像（Landsat）進行不同時期與區域之碳吸存的評估，與以往研究之最大差異為可進行大尺度與多時期的碳吸存評估，並且達到經濟、準確、有效提升效率之目標。 本研究根據光能利用率（Light use efficiency）為基礎模型，計算2005-2010之植生淨初級生產量（Net Primary Productivity, NPP），且配合不同的研究區域：台北、高雄，進一步探討不同的氣候條件與土地利用的條件下，其差異性對於NPP之影響。 成果顯示，在不同環境條件下碳吸存能力受到氣候條件影響最大，且在資料具有缺漏狀態下，依然能反映不同區域之趨勢，雖無法有效評估年總量，但仍可供評估區域性碳吸存能力之趨勢。 / Since the industrial revolution, with the rapid progress of science and technology, population, economy, and medical technology also grow rapidly. Because of increased human demand, coupled with burning lots of fossil fuels, and large-scale felling of tropical rain forests, which result in a significant increase in atmospheric carbon dioxide, and then trigger the greenhouse effect to occur, hence causing global climate change. Under the global warming condition, the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol (KC) both clearly affirmed that forests can fix the main greenhouse gas—carbon dioxide. Because forests have the ability to absorb and store carbon dioxide, they plan an important role in carbon cycle function for ecosystem. If we can effectively monitor forest resources, we will be able to manage greenhouse gases, and can come up with effective control methods. In the present study, we will use remote sensing technology to monitor carbon sequestration and environmental changes. Using Landsat images, we assessed carbon sequestration of different time periods and areas. The biggest difference between this study and previous researches is that large-scale and multi-temporal carbon sequestration assessment can be done, and the goals of economic, accurate, and increasing efficiency can be achieved. In this study, the Net Primary Productivity (NPP) of 2005-2010 was calculated based on the light use efficiency model. By comparing the results of different research areas—Taipei and Kaohsiung, the effects of different climatic conditions and land use conditions on NPP was investigated. The results show that, under different environmental conditions, the carbon sequestration capacity is affected the most by climatic conditions. Furthermore, in the absence of data, it still can reflect the trend of different regions. Although not being able to effectively assess the total amount of a year, it still can be used to assess the trend of regional carbon sequestration capacity.

This thesis investigates the abiotic control of carbon (C) and water vapour fluxes (FCO₂ and E, respectively) in a New Zealand Pinus radiata D. Don plantation and a nearby clearcut. It concentrates on the limitation of these fluxes imposed by growing season soil water deficit. This results from low precipitation (658 mm a⁻¹) in combination with a limited root zone water storage capacity of the very stony soil (> 30% by volume). The thesis analyses results from seven eddy covariance flux measurement campaigns between November 1994 and March 1996. The study site was located in Balmoral Forest, 100 km north-west of Christchurch (42° 52' S, 172° 45' E), in a (in November 1994) 8-year-old stand. One set of measurements was conducted in an adjacent clearcut. Ecosystem flux measurements were accompanied by separate measurements of ground fluxes and of the associated environmental variables. Flux analysis focussed on the underlying processes of assimilation (Ac), canopy stomatal conductance (Gc) and respiration (Reco), using biophysical models coupled to soil water balance and temperature subroutines. Aiming to link time inegrated net ecosystem C (NEP) to tree growth, sequestration in tree biomass (NPP) was quantified by regular measurements of stem diameter using allometric relationships. Average rates of FCO₂ and E were highest in spring (324 mmol m⁻² d⁻¹ and 207 mol m⁻² d⁻¹, respectively) when the abiotic environment was most favourable for Gc and Ac. During summer, fluxes were impeded by the depletion of available soil water (θ) and the co-occurrence of high air saturation deficit (D) and temperature (T) and were equal or smaller than during winter (FCO₂ = 46 mmol m⁻² d⁻¹ in summer and 115 mmol m⁻² d⁻¹ in winter; E = 57 and 47 mol m⁻² d⁻¹, respectively). With increasingly dry soil, fluxes and their associated ratios became predominantly regulated by D rather than quantum irradiance, and on particularly hot days the ecosystem was a net C source. Interannually, forest C and water fluxes increased strongly with rainfall, and the simultaneously reduced D and T. For two succeeding years, the second having 3 % more rain, modelled NEP was 515 and 716 g C m⁻² a⁻¹, Ac 1690 and 1841 g C m⁻² a⁻¹ and Reco 1175 and 1125 g C m⁻² a⁻¹. NEP / E increased in wetter (and cooler) years (1.3 and 1.5 g kg⁻¹), reflecting a relatively larger gain in NEP. Responding mainly to increased rainfall during commonly dry parts of the year (ie summer), and reflecting the otherwise benign maritime climate of New Zealand, NEP during the winter months could exceed NEP during the middle of the notional tree growing season. Annual Ac, NEP, and NPP were strongly linearly related. This relation did not hold during bi-weekly periods when the processes of intermediate C storage were influential. Separate knowledge of tree growth and C fluxes allowed quantification of autotrophic, and heterotrophic respiration (Rhet≈ 0.4 NEP), as well as fine-root turnover (≈0.2 NEP). The ratio of NEP and stem volume growth was conservative (0.24 t C m⁻³) and allows a direct connection to be made between ecosystem carbon fluxes and forest yield tables. In the absence of living roots, the clearcut flux measurements demonstrated the expected limitation of Rhet by soil temperature (Ts) and θ. However, an additional 'pumping effect' was discovered at the open site whereby turbulence increased CO₂ efflux considerably when the soil surface was wet. Accounting for the combined effects of Ts, θ and turbulence, annual Rhet at the clear-cut site (loss to the atmosphere) was »50 % of NEP (C sequestered from the atmosphere) in the nearby forest. Clearly, there is an important contribution of C fluxes during early stages of ecosystem development to the total C sequestered over the lifetime of a plantation.