Short rotation woody crops (SRWC) are bred for rapid growth properties. Knowledge of how varying environmental conditions and endophytic bacteria impact physiology are needed to make planting recommendations. Three eastern cottonwood (EC) and three hybrid poplar (HP) varietals were planted in replicate blocks at upland and alluvial sites. Whole-tree water use and water use efficiency (WUE) were measured using heat-dissipation sap flow and related to overall productivity. Productivity measurements were higher at the upland site. Sap flow was higher at the upland site and for endophyte treated individuals. WUE was higher at the alluvial site and for EC. WUE and leaf area index (LAI) were significantly correlated with biomass (negatively and positively respectively). Overall, HP performed better at the upland site, EC at the alluvial site. These results are beneficial in further testing of optimal site and genotype pairings for SRWC.

No description available.

No description available.

No description available.

No description available.

The overall objectives of this dissertation were to (1) determine whether leaf area index (LAI) (Chapter 2), as well as stem density and height to live crown (Chapter 3) can be estimated accurately in intensively managed pine plantations using small-footprint, multiple-return airborne laser scanner (lidar) data, and (2) ascertain whether leaf area index in temperate mixed forests is best estimated using multiple-return airborne laser scanning (lidar) data or dual-band, single-pass interferometric synthetic aperture radar data (from GeoSAR) alone or both in combination (Chapter 4). In situ measurements of LAI, mean height, height to live crown, and stem density were made on 109 (LAI) or 110 plots (all other variables) under a variety of stand conditions. Lidar distributional metrics were calculated for each plot as a whole as well as for crown density slices (newly introduced in this dissertation). These metrics were used as independent variables in best subsets regressions with LAI, number of trees, mean height to live crown, and mean height (measured in situ) as the dependent variables. The best resulting model for LAI in pine plantations had an R2 of 0.83 and a cross-validation (CV) RMSE of 0.5. The CV-RMSE for estimating number of trees on all 110 plots was 11.8 with an R2 of 0.92. Mean height to live crown was also well-predicted (R2 = 0.96, CV-RMSE = 0.8 m) with a one-variable model. In situ measurements of temperate mixed forest LAI were made on 61 plots (21 hardwood, 36 pine, 4 mixed pine hardwood). GeoSAR metrics were calculated from the X-band backscatter coefficients (four looks) as well as both X- and P-band interferometric heights and magnitudes. Both lidar and GeoSAR metrics were used as independent variables in best subsets regressions with LAI (measured in situ) as the dependent variable. Lidar metrics alone explained 69% of the variability in temperate mixed forest LAI, while GeoSAR metrics alone explained 52%. However, combining the LAI and GeoSAR metrics increased the R2 to 0.77 with a CV-RMSE of 0.42. Analysis of data from active sensors shows strong potential for eventual operational estimation of biophysical parameters essential to silviculture. / Ph. D.

Loblolly pine is an important managed tree species within the southeastern United States, and better understanding spatial patterns in its productivity has potential to contribute to both modeling and management of the species. Using recently-created pine management maps specific to Virginia and empirical relationships predicting pine LAI from the Landsat satellite, we conducted a statewide analysis of temporal patterns in stand-level southern pine leaf area index (LAI) following clear-cut and planting. Here, using 28 years of Landsat time-series data for 13,140 stands that were clear-cut between 2014-2017, we examined 1) when LAI peaked over the rotation, and 2) how LAI in each stand compared to a recommended fertilization threshold of 3.5 LAI. We found that, on average, winter LAI reached a maximum of 2.02., which can be approximately doubled to give a summer LAI of 4.04, and within stand peak occurred between years 13 and 15. We also found that around 45.8% of stands achieved an LAI value higher than 3.5: a fertilization threshold recommended for managed stands in Virginia. The dataset produced by our analysis will bolster information required for modeling loblolly pines as a plant functional type in regional land simulations, and the finding that most stands are below the recommended LAI fertilization threshold will fuel further management-motivated research. / Master of Science / Management of pines in the southeastern U.S. contributes to the region's economy and carbon sequestration potential. In this study, we used Virginia forest harvest maps to identify individual patches (stands) of pine forest which had each gone through a full harvest life cycle (rotation). With unique managed pine stands identified, we used satellite imagery to estimate growth of canopy leaf area over time within each stand, using a metric called leaf area index (LAI). We identified 13,140 separate stands, each with up to 28 years of available data. We took the first full-state census of areas of managed pines in Virginia, and their leaf area development. We acquired one LAI measurement from February of each year, for each stand in Virginia. Using February LAI for each of our stands, we found that an average stand in VA has a maximum winter LAI of 2.02 (meaning an approximate maximum summer LAI of 4.04), and that stands generally reached their peak LAI after around 14 years of growth. It is recommended, in VA, that a landowner fertilize their stand in the middle of a harvest rotation if summer peak LAI is under 3.5, at stand closure. We found that at ten years of stand age, 45.8% of stands were estimated to reach above this threshold. Since this study's dataset is the most comprehensive LAI dataset for managed pines in VA, it may be used to improve management outcomes as well as understand pine productivity for land surface modeling purposes.

Double cropping soybean after small grain harvest does not always allow sufficient canopy growth to maximize photosynthesis and seed yield. This is due to a shorter growing season and moisture deficits common to the Mid-Atlantic USA. Leaf area index (LAI) is the ratio of unit leaf area of a crop to unit ground area and is a reliable indicator of leaf area development and crop biomass. An LAI of 3.5 to 4.0 by flowering is required to maximize yield potential. Soybean LAI will vary within and between fields due to soil differences, cultivar selection, and other cultural practices. Site-specific management strategies such as varying plant population may be used to manipulate LAI and increase yield in leaf area-limited systems. Furthermore, methods to remotely sense leaf area are in order to facilitate such management strategies in large fields. The objectives of this research were to: i) determine the effect of plant population density on soybean LAI and yield; ii) determine the relationship between LAI measured at different reproductive stages and yield; iii) investigate and validate relationships between LAI and yield for two cultivars in three crop rotations across varying soil moisture regimes; iv) validate relationships found in previous work between soybean LAI and yield across soil moisture regimes in grower fields; and v) determine if normalized difference vegetation index (NDVI) values obtained from aerial infrared images can be used to estimate LAI and soybean yield variability. Increasing plant population increased LAI for cultivars at Suffolk in 2000 and 2001, but LAI increased with plant populations on soils with lower plant available water holding capacity (PAWHC) at Port Royal in 2001. In 2000 at Suffolk, seed yield increased quadratically with increasing population and cultivar did not affect the response. In 2001, no relationship occurred between yield and plant population at either Suffolk or Port Royal, but the relationship of yield and LAI depended on soybean development stage at both sites. However, this relationship was not consistent between sites or years. In another study, crop rotation affected LAI and yield one out of two years. However, LAI and yield in both study years were negatively impacted on soil types with lower PAWHC. Where significant, a linear relationship was observed between yield and LAI for all soil types. Studies on grower fields showed similar linear relationships between yield and LAI. Remote sensing techniques showed promise for estimation of LAI and yield. When obtained at an appropriate development stage, vegetation indices correlated to both LAI and yield, and were observed to be effective as a predictor of LAI until plants achieved LAI levels of 3.5 to 4.0. / Master of Science

Master of Science / Department of Agronomy / Robert M. Aiken / Increasing crop water use efficiency (WUE), the amount of biomass produced per unit water consumed, can enhance crop productivity and yield potential. The objective of the first study was to evaluate the factors affecting water productivity among eight sorghum (Sorghum bicolor (L.) Moench) genotypes, which differ in canopy architecture. Sorghum genotypes, grown under field conditions, showed significant differences in (a) biomass production, (b) water use, (c) intercepted radiation, (d) water productivity and (e) radiation use efficiency (RUE; the amount of biomass produced per unit of intercepted radiation which is suitable for photosynthesis). WUE and RUE were more strongly correlated to biomass production than to water use or intercepted radiation, respectively. RUE was positively correlated to WUE and tended to increase with internode length, the parameter used to characterize canopy architecture. These results demonstrate that increased utilization of radiation can increase water productivity in plants. Sorghum canopies that increase light transmission to mid−canopy leaves can increase RUE and also have the potential to increase crop productivity and WUE. The objective of the second study was to develop a quantitative model to predict leaf area index (LAI), a common quantification of canopy architecture, for sorghum from emergence to flag leaf stage. LAI was calculated from an algorithm developed to consider area of mature leaves (leaves with a ligule/collar), area of expanding leaves (leaves without a ligule/collar), total leaf area per plant and plant population. Slope of regression of modeled LAI on observed LAI varied for photoperiod sensitive (PPS) and insensitive (non−PPS) genotypes in 2010. A good correlation was found between the modeled and observed LAI with coefficient of determination (R[superscript]2) 0.96 in 2009 and 0.94 (non−PPS) and 0.88 (PPS) in 2010. These studies suggest that canopy architecture has prominent influence on water productivity of crops and quantification of canopy architecture through an LAI simulation model has potential in understanding RUE, WUE and crop productivity.

ABSTRACT Assessing the impact of herbivory on plant growth and reproduction is important to predict the success of biocontrol of invasive plants. Leaf area production is most important, as photosynthesis provides the foundation for all plant growth and fitness. High levels of defoliation generally reduce the productivity of plants. However, leaf area production fluctuates during the season and compensational growth may occur, which both complicate accurate estimations of defoliation impacts. Under field conditions the interaction with neighbouring species and the availability of soil nutrients need to be assessed in order to gauge long term effects of weed invasions on natural environments. In this thesis I have investigated seasonal leaf area dynamics in Buddleia davidii following repeated artificial defoliation, to quantify compensational leaf production and to understand the regulatory mechanisms involved. The impact of defoliation on photosynthesis, seed production, germination and nitrogen translocation patterns were analysed. Finally, possible facilitation between B. davidii and a native nitrogen fixer, Coriaria arborea, and the impact of B. davidii on soil nutrient availability were investigated. In defoliated B. davidii, increased node production (34%), leaf size (35%) and leaf longevity (12%) resulted in 52% greater total emergent leaf area in the short term. However, with time and diminishing tissue resources the compensation declined. No upregulation of photosynthesis was observed in pre-existing leaves. Compensational leaf area production occurred at the expense of reproduction but the germination capacity of individual seeds was unaffected. In B. davidii, nitrogen reserves are stored in old leaves. Thus, the defoliation-induced decline in tissue reserves led to changes in the remobilisation pattern and increased the importance of soil uptake but biomass production especially that of roots had declined significantly (39%). Slight facilitation effects from the neighbouring nitrogen fixer and VA-mycorrhizae were observed on B. davidii in the field, while its impact on soil chemistry during spring was negligible. Defoliation of B. davidii resulted in priority allocation of resources to compensational leaf growth and a concomitant reduction in flower and seed production. The compensational leaf production greatly increased the demand for nitrogen, while continued leaf removal decreased the pool of stored nitrogen. This led to changes in nitrogen remobilisation and an increased importance of root uptake. However, the significant decline in root growth will likely impair adequate nutrient uptake from the soil, which is especially important where B. davidii invades nutrient poor habitats and will increase the success of biocontrol of the species. While mycorrhizae increase nutrient accessibility for B. davidii, it is likely that the additional stress of defoliation will negate the small facilitative effects from nitrogen-fixing species like C. arborea. This research provides new insights into the mechanisms regulating leaf area dynamics at the shoot level and systemic physiological responses to defoliation in plants, such as nitrogen translocation. The compensation in leaf area production was considerable but only transitory and thus, the opportunity to alleviate effects of leaf loss though adjustment of light capture limited. However, to ascertain that photosynthesis at whole plant level does not increase after defoliation, more detailed measurements especially on new grown leaves are necessary. In general, defoliation had greatly reduced plant growth and performance so that an optimistic outlook for controlling this species can be given. Conclusions about the wider impacts of B. davidii on soil chemistry and community function will require further research.