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1.  Is leaf dry matter content a better predictor of soil fertility than specific leaf area? 
Annals of Botany  2011;108(7):1337-1345.
Background and Aims
Specific leaf area (SLA), a key element of the ‘worldwide leaf economics spectrum’, is the preferred ‘soft’ plant trait for assessing soil fertility. SLA is a function of leaf dry matter content (LDMC) and leaf thickness (LT). The first, LDMC, defines leaf construction costs and can be used instead of SLA. However, LT identifies shade at its lowest extreme and succulence at its highest, and is not related to soil fertility. Why then is SLA more frequently used as a predictor of soil fertility than LDMC?
SLA, LDMC and LT were measured and leaf density (LD) estimated for almost 2000 species, and the capacity of LD to predict LDMC was examined, as was the relative contribution of LDMC and LT to the expression of SLA. Subsequently, the relationships between SLA, LDMC and LT with respect to soil fertility and shade were described.
Key Results
Although LD is strongly related to LDMC, and LDMC and LT each contribute equally to the expression of SLA, the exact relationships differ between ecological groupings. LDMC predicts leaf nitrogen content and soil fertility but, because LT primarily varies with light intensity, SLA increases in response to both increased shade and increased fertility.
Gradients of soil fertility are frequently also gradients of biomass accumulation with reduced irradiance lower in the canopy. Therefore, SLA, which includes both fertility and shade components, may often discriminate better between communities or treatments than LDMC. However, LDMC should always be the preferred trait for assessing gradients of soil fertility uncoupled from shade. Nevertheless, because leaves multitask, individual leaf traits do not necessarily exhibit exact functional equivalence between species. In consequence, rather than using a single stand-alone predictor, multivariate analyses using several leaf traits is recommended.
PMCID: PMC3197453  PMID: 21948627
Ellenberg numbers; functional traits; leaf density; leaf nitrogen; leaf size; leaf thickness; relative growth rate (RGR); shade tolerance; variation in trait expression
2.  Stomatal vs. genome size in angiosperms: the somatic tail wagging the genomic dog? 
Annals of Botany  2010;105(4):573-584.
Background and Aims
Genome size is a function, and the product, of cell volume. As such it is contingent on ecological circumstance. The nature of ‘this ecological circumstance’ is, however, hotly debated. Here, we investigate for angiosperms whether stomatal size may be this ‘missing link’: the primary determinant of genome size. Stomata are crucial for photosynthesis and their size affects functional efficiency.
Stomatal and leaf characteristics were measured for 1442 species from Argentina, Iran, Spain and the UK and, using PCA, some emergent ecological and taxonomic patterns identified. Subsequently, an assessment of the relationship between genome-size values obtained from the Plant DNA C-values database and measurements of stomatal size was carried out.
Key Results
Stomatal size is an ecologically important attribute. It varies with life-history (woody species < herbaceous species < vernal geophytes) and contributes to ecologically and physiologically important axes of leaf specialization. Moreover, it is positively correlated with genome size across a wide range of major taxa.
Stomatal size predicts genome size within angiosperms. Correlation is not, however, proof of causality and here our interpretation is hampered by unexpected deficiencies in the scientific literature. Firstly, there are discrepancies between our own observations and established ideas about the ecological significance of stomatal size; very large stomata, theoretically facilitating photosynthesis in deep shade, were, in this study (and in other studies), primarily associated with vernal geophytes of unshaded habitats. Secondly, the lower size limit at which stomata can function efficiently, and the ecological circumstances under which these minute stomata might occur, have not been satisfactorally resolved. Thus, our hypothesis, that the optimization of stomatal size for functional efficiency is a major ecological determinant of genome size, remains unproven.
PMCID: PMC2850795  PMID: 20375204
Stomatal size; genome size; seed size; life history; photosynthesis; allometry; ecology; evolution; SLA; leaf structure; CAM; C4
3.  Seasonal Branch Nutrient Dynamics in Two Mediterranean Woody Shrubs with Contrasted Phenology 
Annals of Botany  2004;93(6):671-680.
• Background and aims Mediterranean woody plants have a wide variety of phenological strategies. Some authors have classified the Mediterranean phanaerophytes into two broad phenological categories: phenophase‐overlappers (that overlap resource‐demanding activities in a short period of the year) and phenophase‐sequencers (that protract resource‐demanding activities throughout the year). In this work the impact of both phenological strategies on leaf nutrient accumulation and retranslocation dynamics at the level of leaves and branches was evaluated. Phenophase‐overlappers were expected to accumulate nutrients in leaves throughout most of the year and withdraw them efficiently in a short period. Phenophase‐sequencers were expected to withdraw nutrients progressively throughout the year, without long accumulation periods.
• Methods To test this hypothesis, variations in phenology and leaf NPK in the crown of a phenophase‐overlapper Cistus laurifolius and a phenophase‐sequencer Bupleurum fruticosum were monitored monthly during 2 years.
• Key Results Changes in nutrient concentration at the leaf level were not clearly related with the different phenologies. Nitrogen and phosphorous resorption efficiencies were lower in the phenophase‐overlapper, and accumulation–retranslocation seasonality was similar in both species. Changes in the branch nutrient pool agreed with the hypothesis that the phenophase‐overlapper accumulated nutrients from summer until the bud burst of the following spring, recovering a large nutrient pool during massive leaf shedding. The phenophase‐sequencer did not accumulate nutrients from autumn until early spring, achieving lower nutrient recovery during spring leaf shedding.
• Conclusions It is concluded that phenological demands influence branch nutrient cycling. This effect is easier to detect by assessing changes in the branch nutrient pool rather than changes in the leaf nutrient concentration.
PMCID: PMC4242299  PMID: 15072979
Phenology; Mediterranean climate; phenophase‐sequencers; phenophase‐overlappers; nutrients; resorption efficiency; Cistus laurifolius; Bupleurum fruticosum

Results 1-3 (3)