No detectable aerobic methane efflux from plant material, nor from adsorption/desorption processes

In early 2006, Keppler et al. (Nature, 439:187–191) reported a novel finding that plant leaves, and even simple organic materials, can release methane under aerobic conditions. We investigated here whether the reported methane release might simply arise from methane desorption from sample surfaces after prior exposure to higher methane concentrations. We exposed standard cellulose filter papers (i.e. organic material with a high surface area) to atmospheric methane concentration and then transferred them to a low-methane atmosphere. Our results suggest that any desorption flux was extremely small (−0.0001±0.0019 ngCH<sub>4</sub> kgDW<sup>−1</sup> s<sup>−1</sup>) and would play no quantitatively significant role in modifying any measured methane fluxes. <br> <br> We also incubated fresh detached leaves of several species and intact <i>Zea mays</i> seedlings under aerobic and low-light conditions. After correcting for a small measured methane influx into empty chambers, measured rates of methane emission by plant materials were zero or, at most, very small, ranging from −0.25±1.1 ngCH<sub>4</sub> kgDW<sup>−1</sup> s<sup>−1</sup> for <i>Zea mays</i> seedlings to 0.10±0.08 ngCH<sub>4</sub> kgDW<sup>−1</sup> s<sup>−1</sup> for a mixture of freshly detached grasses. These rates were much smaller than the rates originally reported by Keppler et al. (2006)

Photosynthesis and transpiration in a dry-land Pinus radiata forest

This thesis investigates biotic and abiotic regulation of photosynthesis and transpiration at the leaf and canopy scales in a dry-land Pinus radiata D. Don forest by combining gas exchange measurements with biophysical process-based models of photosynthesis, radiation transfer, and soil water balance. Responses of photosynthesis to leaf intercellular CO₂ concentration in two-year old P. radiata seedlings were measured at a range of temperatures and leaf nitrogen concentrations in order to quantify parameters describing photosynthetic capacity and temperature response in a biophysical model of C₃ photosynthesis. Increasing leaf temperature from 8 °C to 30 °C caused a four-fold increase in Vcₘₐₓ the maximum rate of carboxylation (10.7 to 43.3 μmol m⁻² s⁻¹), and a three-fold increase in Jₘₐₓ, the maximum electron transport rate (20.5 to 60.2 μmol m⁻² s⁻¹). Foliar nitrogen concentration (N) varied between 0.36 mmol g⁻¹ and 1.27 mmol g⁻¹, and there were linear relationships between N and both Vcₘₐₓ and Jₘₐₓ. Measurements made throughout the crown of a forest tree, where N varied from 0.83 mmol g⁻¹ near the base to 1.54 mmol g⁻¹ near the leader, yielded similar relationships. The leaf-level photosynthesis model was combined with a water balance model to successfully explain a seasonal pattern in stable carbon isotope composition (δ¹³C) measured within annual rings of P. radiata from two sites which differed markedly in annual water balance. Over two growing seasons there was good agreement between mean canopy-level cᵢ derived from the tree-ring δ¹³C data and modelled leaf-level cᵢ levels. The amplitudes of seasonal δ¹³C variation at the wet and dry sites were 1-2 %₀ and 4 %₀ respectively, and mean δ¹³C values from the wet site were 3 %₀ more ¹³C depleted than those from the dry site implying lower water-use efficiency (carbon assimilation per unit transpiration). Seasonal variation in carbon isotope discrimination of leaves in the canopy is therefore reflected directly in the δ¹³C of stem wood. A canopy photosynthesis model was developed by combining the leaf-level model with a model of canopy radiation transfer, and used as a framework to analyse a field experiment designed to quantify the response of photosynthesis and tree growth to a long-term reduction in illuminated leaf area. Shading the lower crown of two young forest trees reduced absorbed radiation and canopy photosynthesis by 11 and 9 % respectively in the first year. Nitrogen was translocated from current year foliage below the shade cloth to that above, and carbon partitioning to the branches increased at the expense of stem growth. In the second year, the effect of the shading on absorbed radiation, canopy photosynthesis and tree growth was less due to a reduction in shaded foliage proportional to total leaf area. Additionally, a prolonged period of soil water deficit during the summer of year 2 reduced photosynthesis, stomatal conductance and growth similarly in both shaded and control trees. Models which scale up processes from the leaf-level to the canopy can provide a framework to analyse and interpret field experiments

A process-based model of conifer forest structure and function with special emphasis on leaf lifespan

We describe the University of Sheffield Conifer Model (USCM), a process-based approach for simulating conifer forest carbon, nitrogen, and water fluxes by up-scaling widely applicable relationships between leaf lifespan and function. The USCM is designed to predict and analyze the biogeochemistry and biophysics of conifer forests that dominated the ice-free high-latitude regions under the high pCO2 “greenhouse” world 290–50 Myr ago. It will be of use in future research investigating controls on the contrasting distribution of ancient evergreen and deciduous forests between hemispheres, and their differential feedbacks on polar climate through the exchange of energy and materials with the atmosphere. Emphasis is placed on leaf lifespan because this trait can be determined from the anatomical characteristics of fossil conifer woods and influences a range of ecosystem processes. Extensive testing of simulated net primary production and partitioning, leaf area index, evapotranspiration, nitrogen uptake, and land surface energy partitioning showed close agreement with observations from sites across a wide climatic gradient. This indicates the generic utility of our model, and adequate representation of the key processes involved in forest function using only information on leaf lifespan, climate, and soils

Computer Reconstruction of Plant Growth and Chlorophyll Fluorescence Emission in Three Spatial Dimensions

Plant leaves grow and change their orientation as well their emission of chlorophyll fluorescence in time. All these dynamic plant properties can be semi-automatically monitored by a 3D imaging system that generates plant models by the method of coded light illumination, fluorescence imaging and computer 3D reconstruction. Here, we describe the essentials of the method, as well as the system hardware. We show that the technique can reconstruct, with a high fidelity, the leaf size, the leaf angle and the plant height. The method fails with wilted plants when leaves overlap obscuring their true area. This effect, naturally, also interferes when the method is applied to measure plant growth under water stress. The method is, however, very potent in capturing the plant dynamics under mild stress and without stress. The 3D reconstruction is also highly effective in correcting geometrical factors that distort measurements of chlorophyll fluorescence emission of naturally positioned plant leaves

Development of an environmental effects and tourist flow data management system

There is increasing concern about the environmental sustainability of tourism based on natural attractions. We have developed a preliminary computer-based data management system that integrates information about tourists and their use of natural assets with information about how indicators of asset health respond to increasing visitor numbers. First, we collected data on tourist flows between demand (natural attractions) and supply (visitor nodes) sites for the West Coast of New Zealand. Second, we studied a variety of natural asset types in an attempt to develop models describing relationships between visitor numbers and impacts from these visits. These data were then combined to produce the environmental effects and tourism flows data management system for the West Coast. We modelled tourist flows to a range of assets, including the Franz Josef and Fox glaciers, Lake Matheson, the Okarito white heron colony, Pancake Rocks, the Cape Foulwind seal colony and a range of caves in the Buller area. Some assets, e.g., the white heron colony, are already nearing biophysical capacity, while others are not, e.g., the glaciers.This research was funded by the Foundation for Research, Science and Technology under contract LINX0007

Forest and shrubland canopy carbon uptake in relation to foliage nitrogen concentration and leaf area index: a modelling analysis

A multi-layer canopy model was used to simulate the effects of changing foliage nitrogen concentration and leaf area index on annual net carbon uptake in two contrasting indigenous forest ecosystems in New Zealand, to reveal the mechanisms regulating differences in light use efficiency. In the mature conifer-broadleaved forest dominated by Dacrydium cupressinum, canopy photosynthesis is limited principally by the rate of carboxylation associated with low nutrient availability. Photosynthesis in the secondary successional Leptospermum scoparium/Kunzea ericoides shrubland is limited by electron transport. Maximum carbon uptake occurred in spring at both sites. Annual increases in canopy photosynthesis with simulated increases up to 50% in leaf area index, L, or foliage nitrogen concentration per unit foliage area, Na, were largely offset by increases in night-time respiration. A realistic simulation where L was increased by 50% and Na by 20% together (equivalent to an increase in total canopy nitrogen of 80%) led to decreases in net annual carbon uptake because the increase in photosynthesis was offset by the increase in respiration. Given the environmental constraints, both canopies in their natural states appear to be operating at the optimum conditions of leaf area index and nitrogen concentration for maximum net carbon uptake.Assimilation de carbone par une canopée forestière et une végétation buissonnante en relation avec l’indice foliaire et les teneurs en azote : un exercice de modélisation. Un modèle multi couche de canopée forestière a été utilisé pour simuler les effets de changements des teneurs en azote foliaire et d’indice foliaire sur le bilan net annuel d’assimilation de carbone dans deux écosystèmes forestiers contrastés de Nouvelle Zélande, afin de révéler les mécanismes de régulation et de contrôle d’efficience d’utilisation de la lumière par les canopées. Dans la forêt primaire mixte conifère feuillue dominée par Dacrydium cupressinum, l’assimilation de carbone de la canopée est limité par la carboxylation, essentiellement du fait d’une faible disponibilité en éléments minéraux. Cette assimilation est limitée par le transport d’électrons photosynthétiques dans le cas du peuplement buissonnant secondaire à base de Leptospermum scoparium/Kunzea ericoides. Le maximum d’assimilation de carbone se produit au printemps dans les deux cas. Au cours de l’année, les gains induits dans la photosynthèse par des augmentations simulées d’indice foliaire de 50 % ont été largement contrebalancés par les pertes dues à l’augmentation de respiration nocturne. Une simulation réaliste dans laquelle l’indice foliaire était augmenté de 50 % et l’azote foliaire de 20 % (ce qui correspond à une augmentation de 10 % de l’azote total de la canopée) a conduit à une baisse du gain de carbone cumulé sur l’année. Étant données les contraintes imposées par l’environnement, les deux couverts semblent fonctionner à l’optimum de leur indice foliaire et de leur concentration en N et maximisent ainsi le gain annuel de carbone