Leaf life span and nutrient resorption as determinants of plant nutrient conservation in temperate‐arctic regions

Abstract

Nutrient conservation plays an important role in plants adapted to infertile environments. Nutrients can be conserved mainly by extending the life span of plant parts and\or by minimizing the nutrient content of those parts that are abscissed. Together these two parameters (life span and resorption) define the mean residence time (MRT ) of a nutrient. In this review we summarize available information on nitrogen resorption and life span, and evaluate their relationship to the MRT of nitrogen, both between and within species. Abundant information with respect to nitrogen resorption efficiency and life span is available at the leaf level. By definition, woody evergreen plants have a much longer leaf life span than species of other life-forms. Conversely, differences in resorption efficiency among life-forms or among plants in habitats differing in soil fertility appear to be small. Inter-specific variation in leaf life span is much larger than intra-specific variation (factor of 200 compared with 2, respectively), while resorption efficiency varies by about the same magnitude at both levels (factor of 3.8 compared with 2.7, respectively). The importance of resorption efficiency in determining leaf-level MRT increases exponentially towards and above the maximum resorption efficiency observed in nature. This effect is independent of leaf life span, which may explain the lack of life-form related differences in resorption efficiency. When scaling up from the leaf to the whole-plant level, fundamental differences in turnover rate among different plant organs must be considered. Woody species invest c. 50% of their net productivity into their low-turnover stems, while in herbaceous species the life span of stems is only slightly longer than that of leaves. As a result, nutrient turnover of woody (evergreen and deciduous) plants is generally lower than that of herbaceous species (herbs and graminoids) on a whole-plant basis. At the intra-specific level empirical data show that both biomass life span (i.e. the inverse of biomass loss rate) and resorption efficiency are important sources of variation in MRT. However, we argue that the relative importance of resorption efficiency in explaining variation in MRT is lower at the interspecific level, whereas the reverse is true for life span. This is because variation in MRT and life span is much larger at the inter-specific level compared with variation in resorption efficiency. Plant traits related to nutrient conservation are discussed with respect to their implications for leaf structure, plant growth, competition, succession and ecosystem nutrient cycling.

N availability and mechanisms of N conservation in deciduous and semideciduous tropical forest legume trees

“…A longer leaf life span is regarded as a mechanism for conserving nutrients since it reduces the loss of minerals during leaf abscission (Aerts 1995;Carrera et al 2003;Eckstein et al 1999).…”

“…Therefore, evergreen species are likely to show greater resorption efficiency in comparison to deciduous ones. However, consensus has not been reached in the literature comparing these two groups of plants (Aerts 1996;Lal et al 2001) and attempts to relate nutrient resorption efficiency to soil fertility have led to controversy (Aerts 1996;Eckstein et al 1999;Cordell et al 2001;Carrera et al 2003). Killingbeck (1996) concluded that plants which perform symbiotic N fixation (SNF) presented lower N-resorption proficiency (NRP), and N-resorption efficiency (NRE) than those which do not.…”

Seasonal variability of multiple leaf traits captured by leaf spectroscopy at two temperate deciduous forests

“…For example, LMA rapidly 276 increased in the spring, but showed only a minor decline by the end of the measurement 277 period. N mass was higher (~4-5%) at the start of the season, and remained stable around 2% 278 during the summer, followed by ~1% decrease in the fall, presumably caused by nitrogen 279 resorption (Eckstein et al 1999). Similar to LMA, C mass accumulated 2-4% in the spring 280 and stabilized for the rest of the growing seasons around 50%.…”

Assessment of nutrient use in annual and perennial crops: A functional concept for analyzing nitrogen use efficiency

“…The N productivity was integrated into a concept, in which the NUE was broken down into the two components of N productivity (Ågren 1985) and N carry-over from annual to perennial plant parts, i.e., mean residence time of N (Berendse and Aerts 1987). The mechanistic background of the two components was further analysed and resulted in a number of hypotheses regarding, e.g., the functional relationships between N productivity and conservation mechanisms in plants (Garnier et al 1995;Garnier and Aronson 1998;Eckstein et al 1999). …”

“…In addition, the ecological approaches pay great attention to the evolutionary mechanisms of plant adaptation to nutrient-poor environments and frequently assume that, in an annual perspective, the nutrient uptake equals the nutrient losses (i.e. steady-state conditions, Eckstein et al 1999;Frissel 1981). These conditions are often less relevant in agriculture.…”