Does the Gradualness of Leaf Shedding Govern Nutrient Resorption from Senescing Leaves in Mediterranean Woody Plants? (original) (raw)
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Functional Ecology, 2007
Leaf life span (LLS) is one of the traits involved in the leaf economics spectrum (ranging from fast acquisition to efficient conservation of resources). How it relates to nutrient resorption efficiency ( R EFF ), another key component of resource conservation, is still under debate. Here we test how leaf traits related to leaf economy, mass loss during senescence and R EFF covary among species differing in resource use, and how they respond to nitrogen limitation. 2. Leaf traits were assessed for 18 species differing in successional status and in resource use, grown in a common-garden experiment under limiting and non-limiting N supply. 3. As expected, leaf traits and nutrient R EFF vary with species successional status: early successional species have high rates of resource acquisition with high specific leaf area and live-leaf phosphorus concentrations, whereas late successional species have an efficient nutrient conservation with long LLS and high nutrient R EFF . Leaf life span decreased under non-limiting N conditions, while nitrogen R EFF was unchanged. 4. Leaf mass loss can alter assessment of nutrient R EFF . Nutrient R EFF was controlled by nutrient concentration in dead leaves and hence represents a process, distinct from leaf longevity, that leads to resource conservation.
RESORPTION EFFICIENCY DECREASES WITH INCREASING GREEN LEAF NUTRIENTS IN A GLOBAL DATA SET
Ecology, 2005
To investigate effects of green-leaf nutrient status on senesced-leaf nutrient concentrations and resorption efficiency, we developed a database of nitrogen (N) and phosphorus (P) concentrations in green and senesced leaves from 92 published studies. We fit power functions (i.e., [nutrient] sen ϭ A [nutrient] ) separately for N and P. The database B gr encompassed 297 perennial species of different life-forms. Across these divergent species and conditions, a major control on senesced-leaf nutrient concentration was green-leaf nutrient status; nutrient concentrations in senesced leaves were positively associated with green-leaf nutrient concentrations (r 2 values from 51% to 84%). Within-species variation as well as species differences contributed to the overall variation in nutrient concentrations. Moreover, N and P resorption efficiency decreased, respectively, with increased N and P green-leaf status; fitted power functions indicated that a disproportionate amount of nutrient remained in senesced leaves of higher green-leaf nutrient status. Functional relationships between nutrient concentrations in senesced and green leaves were indistinguishable for evergreen and deciduous species, but evergreens tended to have lower concentrations in both senesced and green leaves. General relationships (across species and environments) between senesced-and green-leaf nutrient concentrations and broad, intraspecific variation in nutrient concentrations suggest that variation in resorption efficiency and proficiency could be a result (and not necessarily a cause) of species sorting across fertility gradients.
2005
Extensive variation in fractional resorption of mineral elements from plant leaves is still not fully understood. In multi-species forest stands, species leaf fall phenology and leaf constitution may significantly modify the timing of nutrient return to the soil and overall plant nutrient loss. We studied leaf fall and nutrient loss kinetics, and leaf composition in three natural, temperate, deciduous broadleaf forest stands to determine the role of timing of leaf abscission and nutrient immobilization in cell walls on nutrient resorption efficiency of senescing leaves. Nitrogen (N), phosphorus and potassium contents decreased continuously in attached leaves after peak physiological activity during mid-season. Changes in nutrient contents of attached leaves were paralleled by decreases in nutrient contents in freshly fallen leaf litter. In different species and for different nutrients, resorption of nutrients from senescing leaves proceeded with different kinetics. The maximum nutrient resorption efficiency (the fraction of specific nutrient resorbed from the leaves at the end of leaf fall) did not depend on the mid-seasonal nutrient concentration. Species with earlier leaf fall resorbed leaf nutrients at a faster rate, partly compensating for the earlier leaf fall. Nevertheless, the litter-mass weighted mean nutrient contents in leaf litter were still larger in species with earlier leaf fall, demonstrating an inherent trade-off between early leaf fall and efficient nutrient resorption. This trade-off was most important for N. Losses of the non-mobile nutrients calcium and magnesium were unaffected by the timing of leaf fall. There was large variation in the maximum N resorption efficiency among species. Correlations among leaf chemical variables suggested that the maximum N resorption efficiency decreased with the increasing fraction of cell walls in the leaves, possibly due to a greater fraction of N occluded in cell wall matrix. We conclude that species leaf fall phenology and leaf chemistry modify the timing and quantities of plant nutrient losses, and that more diverse forest stands supporting a spectrum of species with different phenologies and leaf types produce litter with more variable chemical characteristics than monotypic stands.
Nutrient concentration, resorption and lifespan: leaf traits of Australian sclerophyll species
Functional Ecology, 2003
Most plants withdraw nutrients from leaves as they age, and redeploy them elsewhere in the plant. The proportion of nutrients resorbed and the residual nutrient concentration in senesced leaves are different but complementary indices of nutrient conservation via this process. A major spectrum of strategic variation runs from plant species with typically long leaf lifespan (LL), high leaf mass per area (LMA), low leaf nutrient concentrations, and low photosynthetic capacity, to species with the opposite characteristics. It is unknown to what extent either facet of resorption covaries with the LL-LMA spectrum. 2. Green-leaf and senesced-leaf N and P concentrations were quantified for 73 evergreen species from four sites in eastern Australia (nutrient-rich and nutrient-poor sites in each of two rainfall zones). Leaf nutrient concentrations in green and senesced leaves were negatively correlated with LL across all species and at most sites, especially if N 2fixing species were excluded from analyses involving leaf N. 3. Proportional resorption did not differ with soil nutrients, as has been found elsewhere, nor was it correlated with LL. Green-leaf and senesced-leaf nutrient concentrations were lower for species on poorer soils. A simple model was described in which the proportion of resorbed vs soil-derived nutrients deployed in new leaves is set by the relative cost of nutrients from the two sources. The model provides a prospective explanation for the observed differences between species from nutrient-rich and nutrientpoor habitats. 4. The results from this study provide support for the argument that selection to minimize nutrient losses has affected the residual nutrient concentration in senesced leaves, rather than proportional resorption per se . Further, variation among species in residual nutrient concentration was correlated with one of the key spectra of strategic variation between plant species, the leaf lifespan-LMA axis of variation.
Autumn nutrient resorption and losses in four deciduous forest tree species
Forest Ecology and Management, 2006
Nutrient resorption prior to leaf senescence is an important mechanism of nutrient conservation in forest tree species. However, despite the abundance of literature on the subject, inter-specific comparison of common temperate tree species is complicated by both the variability of resorption efficiency, which is affected by many environmental factors, and methodological differences between the studies, especially in relation to measurements of nutrient losses. This study compares the autumn nutrient resorption and nutrient losses via throughfall and litterfall of N, P, K, S, Mg, Ca, Cu, Fe and Mn in adjacent 40-year-old stands of Quercus robur L., Tilia cordata Mill., Fraxinus excelsior L. and Betula pendula Roth. In addition, the relative susceptibility of leaves to leaching was studied in the laboratory. For all species and elements, except K in ash stands, nutrient losses via throughfall were considerably lower than the losses via litterfall during the sampling period (from the end of August to the middle of October). Nutrient amounts in the throughfall were mostly governed by the susceptibility of the respective species to foliar leaching, which was highest in ash trees, but also depended on nutrient amounts in the pre-senescent leaves. K showed the highest losses via throughfall among the studied elements, 30% of the green leaf content being lost in the ash stand and 8-11% in the other stands. Ash also showed considerable throughfall losses (9-19% of green leaf content) of S, Mn, Mg, Ca and P, while the corresponding losses of these elements in other species were lower in relation to the nutrient content of their foliage. Species with higher amounts of nutrients in the green leaves tended to have higher amounts of nutrients in their litter, but this tendency was not observed for all species and elements. Nutrient resorption efficiency, calculated on leaf area basis, differed among species and was highest for N (ranging from 36% in ash to 69% in birch), P (from 37 in ash to 59% in lime), K (from 38% in ash to 51% in lime) and S (from 31% in ash to 48% in birch). Fe and Cu were the most efficiently withdrawn micronutrients (the amounts resorbed ranging from 7-10% in lime to 20-37% in the other species).
Ecological Applications, 2009
Needle chemical composition was measured and nutrient resorption, nutrient use efficiency (NUE) and other indexes were estimated for 24 months in two contrasting natural Pinus sylvestris L. forests in the western Pyrenees. For each location (Aspurz: 650 m elevation, 7% slope; Garde: 1335 m elevation, 40% slope), there were three reference plots (P0), three with 20 % of the basal area removed (P20) and three with 30 % of the basal area removed (P30). Needle P, Ca and Mg concentrations were higher in Garde but N concentration was higher for Aspurz, without differences for K. Nutrient resorption efficiency of P was higher in Aspurz, of Mg higher in Garde and there were no differences between sites in N and K. Nutrient resorption proficiency was significantly higher in the site with lower soil nutrient availability, i.e., for P, Ca and Mg in Aspurz but N in Garde (no differences in K); this may be an indicator of nutrient conservation strategy. Annual nutrient productivity (A) was higher in all nutrients in Aspurz, whereas the mean residence time (MRT) was higher in Garde in all nutrients but P. NUE was significantly higher in Garde for all nutrients but P, which was more efficiently used in Aspurz. In both sites, N, P and K concentrations were higher in 2002 cohort, Ca in 2000 cohort and maximum Mg was found 2001 cohort. Thinning caused a reduction of Mg concentration in the 2001 cohort in Aspurz, an increase of Ca resorption proficiency in Aspurz and Mg resorption at both sites, and reduction of P, K and Mg nutrient response efficiency (NRE) in Garde. Thinning may have caused an increase of the C:Mg ratio through facilitating the development of more biosynthesis apparatus in a more illuminated canopy, but it seemed not to affect resorption in a significant way. Changes in NRE in Garde after thinning show that forest management can affect how trees use nutrients. Our results indicate that the strategy to optimize NUE is different in each stand. In Aspurz (a Mediterranean ecosystem), pine trees carried out resorption more efficiently, while in Blanco et al. (2009) 3/45
Canadian Journal of Botany, 2001
We examined 90 dry tropical tree species growing on contrasting soil types (relatively infertile Ultisol and more fertile Inceptisol) for leaf traits such as leaf habit, specific leaf mass (SLM, leaf dry mass per leaf area), leaf chemistry (nutrient concentrations and C/N ratios), and nutrient resorption. Across the species, SLM ranged from 4.06 to 15.74 mg·cm -2 in mature leaves and from 2.60 to 15.12 mg·cm -2 in senesced leaves. Mature leaf N and P concentrations varied from 0.86% to 4.11% and 0.13% to 0.21%, respectively. Senesced leaf N concentrations varied from 0.49% to 1.90% and P from 0.04% to 0.47%. Resorption efficiencies varied from 26% to 83% (mean = 58.32% ± 1.20%) for N and from 16% to 80% (mean = 49.57% ± 1.48%) for P indicating that the woody species of dry tropical environments resorbed different nutrients in substantial amounts to support new growth. Deciduous species had greater resorbed nutrient pools and resorption efficiencies than evergreen species. Compared with the nutrient-rich environment, species from the nutrient-poor environment had a lower resorbed P pool and lower resorption efficiencies for N and P, but had similar N and P concentrations in mature leaves. Resorption efficiencies for C, N, and P were generally correlated, suggesting that the resorbed C pool acted as a vehicle for mobilizing nutrients, especially N. Species with a low or high C/N ratio in senesced leaf and a low or high N resorption efficiency occurred in both nutrient-poor and nutrient-rich environments, as well as among deciduous and evergreen leaf habits, indicating individualistic adaptations to optimize the efficiency of nutrient resource use and conservation of the dry tropical woody vegetation.
Trees
Leaf structural and nutrient traits are key attributes of plant ecological strategies, as these traits are related to resource use strategies and plant growth. However, leaf structure and nutrient composition can vary among different habitats, leaf habits or phylogenetic groups. In this study, we measured 13 leaf traits (one structural-leaf mass per area, LMA-and 12 nutrient traits) in 98 Mediterranean woody species growing over a wide range of environmental conditions, with the final aim of discerning the main causes of leaf trait variability. The variance decomposition results show that phylogeny, leaf habit and forest habitat affected in several ways the structural and nutrient traits studied. Leaf nutrient concentrations are strongly positively correlated amongst themselves, and negatively correlated with LMA, in accordance with the "leaf economics spectrum". We found that leaf habit and phylogeny were important causes of variation in LMA and in a broad number of leaf nutrients (i.e. C, N, Mg, S, K), while other micronutrients seemed to be more dependent on the environment (i.e. Cu and Mn). In summary, our study reinforces the existence of the leaf economics spectrum in a Manuscript icrtnaManuscriptariatars riinac icrtiinrncs Postprint of: Trees-Structure and Function 1-14 (2017) In press 2 broad pool of Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context as the main drivers of variability in some leaf structural and nutrient traits.
Leaf physiological traits in relation to resprouter ability in the Mediterranean Basin
Plant Ecology, 2011
In Mediterranean ecosystems, fire is a strong selective agent among plants, and the different post-fire regeneration strategies (e.g. resprouting and non-resprouting) have implications for other plant traits. Because young plants of non-resprouters need to grow quickly and mature well before the next fire, we predict that they should possess leaf traits related to increased efficiency in growth and resource acquisition compared with resprouter species. To test this hypothesis, we measured specific leaf area, leaf nitrogen and carbon concentrations and leaf physiological traits, including gas exchange parameters and chlorophyll fluorescence, in 19 Mediterranean species cultivated in a common garden. Both cross-species and phylogenetically informed analyses suggest that non-resprouters have better physiological performance at the leaf level (i.e. higher photosynthetic capacity) than resprouters. All these results suggest that non-resprouter species are able to take greater advantage for vegetative growth and carbon fixation than resprouters during periods when water is readily available. The contrasted physiological differences between resprouters and non-resprouters reinforce the idea that these two syndromes are functionally different (i.e. they are functional types).