Leaf structure and defence control litter decomposition rate across species and life forms in regional floras on two continents

Abstract

There is some evidence that traits of fresh leaves that provide structural or chemical protection (' defence ') remain operational in the leaf litter and control interspecific variation in decomposition rate in or on the soil. We tested experimentally whether the negative relationship between foliar defence and litter decomposition rate is fundamental, i.e. whether it is seen consistently across higher plant species and life forms, and whether it is repeated in the floras of geographically and climatically distinct areas separated by an ocean. We employed the published results of two outdoor litter bag experiments, in which we simultaneously compared the relative mass losses (' decomposibility ') of leaf litters of a wide range of plant species. One experiment was in Co! rdoba, Argentina, and included 48 Argentine species typical of the dry, subtropical landscapes along a steep altitudinal gradient. The other was in Sheffield, UK, and hosted 72 British species typical of the temperate-Atlantic landscape there. We linked the two experiments through a similar experiment in Sheffield that hosted litters of subsets of both the Argentine and British species. We also tested fresh leaves of all species from the same areas for tensile strength (' toughness ') and relative palatability to generalist herbivorous snails in multi-species ' cafeteria ' experiments. Both in Argentina and in Great Britain there were highly significant correlations between leaf palatability (r l 0.61 ; 0.73) or leaf tensile strength (r l k0.60 ; k0.60) and litter mass loss across all species. These relationships could be explained by variation both between and within broad life-form groups. Specific leaf area (area : dry mass) of fresh leaves was consistently correlated only with litter mass loss within British life form groups. We illustrated the possible ecosystem consequences of these relationships by comparing functional traits of British species differing in leaf habit. In comparison with deciduous species, evergreens generally had innately slow growth, which corresponded to their longer-lived leaves of lower specific leaf area, higher tensile strength and lower palatability to generalist invertebrate herbivores. Correspondingly, evergreens produced more resistant leaf litter. Thus, slow-growing evergreens might maintain their position in infertile ecosystems through leaf traits that help them to conserve their nutrients efficiently and to keep nutrient mineralization low, thereby not allowing potentially fast-growing deciduous species to outcompete them.

Going Back to Basics: Importance of Ecophysiology when Choosing Functional Traits for Studying Communities and Ecosystems

“…Additionally, many of these global proxies reflect multiple aspects of organisms function, which can show distinct and even opposing responses to environmental drivers. This implies that a set of traits that best explains response to environmental factors in large scales are not always the best under local nutrient availability (Reich et al 1992;Wright et al 2004;Chave et al 2009), or good indicators of plant species defense against herbivory and plant effects on litter decomposition (Cornelissen et al 1999). Due to the successful explanation of global patterns of trait variation and the relatively easy measurements, some functional traits have become widely used.…”

Root tissue structure is linked to ecological strategies of grasses

“…Low tissue mass density in leaves is associated with a high specific leaf area, large total leaf area and fast growth, on the one hand (Garnier, 1992 ;Ryser & Lambers, 1995 ;Meerts & Garnier, 1996 ;Ryser & Aeschlimann, 1999), and with short life span and high resource losses on the other (Schla$ pfer & Ryser, 1996 ;Ryser & Urbas, 2000). Leaf toughness and high tensile strength are associated with slow growth and also with a high degree of mechanical stability of the leaves, which tend to be well protected against environmental hazards such as herbivory (Coley, 1983 ;Reich et al, 1991 ;Cornelissen et al, 1999). Hence, tissue mass density is an effective means of predicting the performance of plants along gradients of resource availability (Wilson et al, 1999) ; a low tissue mass density is characteristic of plants of productive habitats, a high tissue mass density is typical in plants of unproductive environments Studies on the ecological significance of tissue structure have mostly been restricted to aboveground organs, especially leaves.…”

The Role of Quantitative Traits of Leaf Litter on Decomposition and Nutrient Cycling of the Forest Ecosystems

“…Low-LMA leaves with high nutrient contents decompose much faster, leading to increased carbon and nutrient cycling (Cornelissen et al 1999;Poorter et al 2009). Community-level LMA had a strong negative impact on the primary productivity and decomposition rate of the successional communities (Poorter et al 2009).…”