Aboveground biomass allocation and water content relationships in Mediterranean trees and shrubs in two climatological regions in Israel

Thisstudy investigated the variation along basipetal gradients of the relationshipsbetween the foliage/wood allocation ratios of biomass and of water content, inMediterranean trees and shrubs, at two different locations along a climaticgradient. Understanding of the biomass allocation and water relations inMediterranean trees and shrubs provides useful information on growth patternsofthese species, and on resource dynamics of these plant communities. Twoexperimental sites were selected along a climatological transect that runs fromthe foothills of the Judean Hills to the northern Negev desert in Israel. Ateach site, 16 quadrats of 10 × 10 m (eight on south-facingslopes and eight on north-facing slopes) were marked. The aboveground biomassofdominant tree and shrub species were estimated. Main branches of trees andshrubs were cut, their foliage and wood biomass were separately weighed, andtheir respective water contents were determined. The species studied includedthe evergreen sclerophylls, Quercus calliprinos, Phillyrealatifolia and Pistacia lentiscus, and thesemi-deciduous species, Cistus creticus, Coridothymuscapitatus and Sarcopoterium spinosum. Theresults indicated that the foliage/wood ratio decreased from the periphery ofthe crown to the interior of the trees and shrubs: foliage biomass and waterwere mainly limited to the top 30 cm of the crown in all studiedspecies. Leaves had higher relative water contents than woody tissues in theupper part of the crown. However; when the whole tree or shrub was considered,the relative water content was found to be mostly allocated to the woodystructures. The results are discussed in terms of biomass allocation in variouslife forms of the eastern-Mediterranean plant communities and how they areaffected by slope aspect and climatic conditions.     

叶龄及树冠不同部位光强对黄花梨光合速率的影响

笔者以黄花梨为试材,研究了叶龄及树冠不同部位光强对其光合速率的影响。结果表明:黄花梨叶片在展叶后约11天即有少量光合产物输出,25天时,单叶净光合速率接近最大值;密植梨树高光合叶幕厚度约125cm左右。     

Some quantitative relationships between leaf area index and canopy nitrogen content and distribution

In a previous study (Yin et al. 2000. Annals of Botany 85: 579-585), a generic logarithmic equation for leaf area index (L) in relation to canopy nitrogen content (N) was developed: L=(1/ktn)1n(1+ktnN/nb). The equation has two parameters: the minimum leaf nitrogen required to support photosynthesis (nb), and the leaf nitrogen extinction coefficient (ktn). Relative to nb, there is less information in the literature regarding the variation of ktn. We therefore derived an equation to theoretically estimate the value of ktn. The predicted profile of leaf nitrogen in a canopy using this theoretically estimated value of ktn is slightly more uniform than the profile predicted by the optimum nitrogen distribution that maximizes canopy photosynthesis. Relative to the optimum profile, the predicted profile is somewhat closer to the observed one. Based on the L-N logarithmic equation and the theoretical ktn value, we further quantified early leaf area development of a canopy in relation to nitrogen using simulation analysis. In general, there are two types of relations between L and N, which hold for canopies at different developmental phases. For a fully developed canopy where the lowest leaves are senescing due to nitrogen shortage, the relationship between L and N is described well by the logarithmic model above. For a young, unclosed canopy (i.e. L < 1.0), the relation between L and N is nearly linear. This linearity is virtually the special case of the logarithmic model when applied to a young canopy where its total nitrogen content approaches zero and the amount of nitrogen in its lowest leaves is well above nb. The expected patterns of the L-N relationship are discussed for the phase of transition from young to fully developed canopies.     

Competition between heather and grasses on Scottish moorlands: Interacting effects of nutrient enrichment and grazing regime

Abstract. Considerable losses and degradation of heathlands (in moorlands and lowlands) have been reported across Europe, with Calluna vulgaris (heather) being replaced by other species, often grasses. Increasing atmospheric nitrogen deposition and overgrazing have been suggested as the driving factors behind this change. This possibility was investigated in a study of the interacting effects of nutrient inputs and grazing on heather and three grass species (Nardus stricta, Deschampsia cespitosa and D. flexuosa) in the field, on a moorland in northeastern Scotland. In addition, the interacting effects of increasing nutrients and Calluna canopy height on N. stricta and D. cespitosa were studied using turves in an outdoor experimental area. In the field, fencing had a larger effect than fertilizer on the growth of all species, except for N. stricta, the species most unpalatable to herbivores. Fencing led to an increase in the height of the Calluna canopy, which may reduce light availability for the grasses. In the turf experiment, the height of the Calluna canopy affected the diameter of the grass tussocks and percentage of green matter (i.e. live leaf material), with plants under the more closed Calluna canopies being smaller. This study suggests that the slow‐growing, evergreen Calluna is a more effective competitor than the faster growing grasses when it has a tall, intact canopy, even at increased levels of nutrient supply. However, overgrazing promotes gap formation in the Calluna canopy, providing an opportunity for grasses to take advantage of increased nutrients. Thus the conservation of heather moorlands requires an understanding of the grazing level which allows Calluna to maintain sufficient canopy structure to outcompete grasses for light.     

Geographical variation in frond size,rootstock density,and sexual reproduction in <Emphasis Type="Italic">Matteuccia struthiopteris</Emphasis> populations in Norway

The main aim of this study was to quantify differences in the structure of dense Matteuccia struthiopteris (L) Todaro among geographically separated populations in Norway, and to relate these differences to variation in environmental variables. A stratified random sampling procedure was applied to select 4 m² quadrats restricted to populations dominated (>75% cover) by the fern. This dimorphic fern can produce three types of leaves (fronds): fertile (sporophyll) and sterile (trophophyll), and in addition also intermediate fronds. In all, 178 populations from different parts of the country were analysed, and in total 9,346 rootstocks were measured. Fifteen percent of the rootstocks were fertile, each producing from one to eight sporophylls, and 2.0% had developed intermediate fronds. Rootstocks with five or more sporophylls were mainly found in Southern Norway. Within the plots, there were major variations in density (10–112), number of small (new) ramets (0–58), total number of sporophylls (0–94) and estimated total fern wet-weight (0.33–22.8 kg). All new additions to the populations were connected to a mother plant (ramets), and none were of sexual origin (genets). The main environmental variables associated with the variation in population structure were mean July temperature (highly correlated with altitude and latitude), mean precipitation and density of the canopy cover. The density of small ramets and number of intermediate fronds increased from south to north. The latitudinal variation in sporophyll development and maximum trophophyll height was best explained by a unimodal model. There were statistically significant differences in the population structure between the eight studied geographic areas in Norway.     

Light distribution and foliage structure in an oak canopy

 Leaf angle distribution and shoot bifurcation ratio were measured and related to photon flux density (PFD) distribution in an oak canopy. Leaf angle distribution deviated substantially from random and changed markedly throughout the canopy. The observed leaf angle distribution was described by an ellipsoidal function with the single parameter of the distribution, x, changing from 1.6 at the top of the canopy to 3.2 in the lowest branches. In vertically homogeneous canopies, the extinction coefficient for diffuse radiation is expected to decline with increasing leaf area index (LAI). However, in the canopy studied here, the leaf angle distribution changed with height such that the effective extinction coefficient remained constant. Both shoot bifurcation ratio and leaf number per shoot declined with decreasing PFD inside the canopy. Based on these observed relationships, a simple canopy growth model that assumes horizontal homogeneity of the canopy was constructed. Calculations showed that a steady state, when growth in the upper of the canopy is in equilibrium with decline of lower canopy, the total canopy LAI should equal to 4.3. This predicted value of equilibrium LAI is larger than that estimated from measurements of PFD transmission (LAI=3.3), but smaller than that directly determined by litter collection (LAI=6.2 in 1998). Possible reasons for these discrepancies are discussed. Received: 22 June 1998 / Accepted: 7 April 1999     

Effects of Elevated CO2 and High Temperature on Single Leaf and Canopy Photosynthesis of Rice

The increase of atmospheric CO2 concentration is indisputable. In such condition, photosynthetic response of leaf is relatively well studied, while the comparison of that between single leaf and whole canopy is less emphasized. The stimulation of elevated CO2 on canopy photosynthesis may be different from that on single leaf level. In this study, leaf and canopy photosynthesis of rice ( Oryza sativa L. ) were studied throughout the growing season. High CO2 and temperature had a synergetic stimulation on single leaf photosynthetic rate until grain filling. Photosynthesis of leaf was stimulated by high CO2, although the stimulation was decreased by higher temperature at grain filling stage. On the other hand, the simulation of elevated CO2 on canopy photosynthesis leveled off with time. Stimulation at canopy level disappeared by grain filling stage in beth temperature treatments. Green leaf area index was not significantly affected by CO2 at maturity, but greater in plants grown at higher temperature. Leaf nitrogen content decreased with the increase of CO2 concentration although it was not statistically significant at maturity. Canopy respiration rate increased at flowering stage indicating higher carbon loss. Shading effect caused by leaf development reached maximum at flowering stage. The CO2 stimulation on photosynthesis was greater in single leaf than in canopy. Since enhanced CO2 significantly increased biomass of rice stems and panicles, increase in canopy respiration caused diminishment of CO2 stimulation in canopy net photosynthesis, keaf nitrogen in the canopy level decreased with CO2 concentration and may eventually hasten CO2 stimulation on canopy photosynthesis. Early senescence of canopy leaves in high CO2 is also a possible cause.