Canopy leaf area constrains [CO ₂ ]-induced enhancement of productivity and partitioning among aboveground carbon pools

Abstract

carbon allocation ͉ global change ͉ nitrogen availability ͉ pine plantation C urrent studies and modeling exercises indicate a very significant role for terrestrial ecosystems in sequestering carbon (C) and potentially mitigating increases in atmospheric CO 2 concentrations ([CO 2 ]) (1, 2), with forests contributing Ϸ80% of terrestrial net primary productivity (NPP) (3). Recent analysis (4) found a surprisingly consistent enhancement of NPP under elevated [CO 2 ] across closed-canopy temperate forest ecosystems ranging greatly in productivity. This study suggested that in forests with low native canopy leaf area index (L), much of the [CO 2 ]-induced enhancement of NPP resulted through an enhancement of L, whereas in forests with mid-to high levels of native L, most of the enhancement of NPP came through an increase in photosynthetic efficiency (4). Several questions deserve further attention: (i) How does the potential for enhancement change with other resource availability (e.g., water and nutrients), and (ii) how is the additional C gained under elevated [CO 2 ] partitioned among C pools of differing longevities? Both questions are crucial to understanding the likely effect of elevated atmospheric [CO 2 ] on long-term C sequestration in forests.Ecosystem productivity shows great spatial and temporal variability. Spatial variability in productivity is most obvious among different ecosystems, resulting from differences in incoming solar radiation, temperature, precipitation, soil properties, and the species adapted to local conditions (5, 6). Variation in forest productivity can occur at much smaller scales, influenced by resource availability (7). In addition, there is often great interannual variability in global and local C sinks within terrestrial ecosystems, which has frequently been linked to climate variability (8, 9). As humans continue to alter their environment by increasing atmospheric [CO 2 ], changing the nitrogen (N) cycle, and contributing to a changing climate, it becomes ever more critical to understand how these changes impact and can possibly be mitigated by terrestrial ecosystems.Forests are generally expected to become greater C sinks as atmospheric CO 2 levels rise (10-12). However, nutrient limitations (13-15) and increasing water deficits with climate change (16, 17) may prevent many forested regions from fully realizing dramatic increases in C sequestration. Interactions of [CO 2 ], available nutrients, and water must be studied to predict C sinks within forests under future conditions and to inform policy and economic guidelines (18). Yet few long-term studies explore the interaction of elevated [CO 2 ] with other growth resources on forest C processes.Much of the spatial and temporal variability in ecosystem productivity is moderated by differences and disruptions in canopy leaf area (L). Canopy L controls light interception and thereby stand productivity (5,19,20). It also affects hydrological processes and thus the dynamics of soil water (21, 22) and litter production, thus the dyn...

The pleiotropic effects of extract containing rhizobial Nod factors on pea growth and yield

“…It was shown that the net primary production of plants is dependent on the leaf area index, which, in turn, is conditional upon nitrogen supply [40]. In our experiments simultaneous increase in nodule number, leaf area and SPAD readings was observed, so taking into consideration the relationship between nitrogen supply and plant productivity [40] it can be assumed that the larger area available for photosynthesis stems from higher nitrogen supply from the nodules. The water use efficiency (WUE) values after Nod factor treatment were worse than in the control group, however, suggesting that changes in the water balance were not detrimental to the plants.…”

The Spatial Factor, Rather than Elevated CO 2 , Controls the Soil Bacterial Community in a Temperate Forest Ecosystem

“…We show that the C/N ratio and total N were potentially important for predicting the variations in soil bacterial diversity, at least at the local scale, where soil pH varied relatively little (4.1 to 5.2) and was uncorrelated to bacterial diversity. Because at this site N acts as a resource that limits plant growth (16,52,60,63), it is not surprising that a positive correlation between total N and soil bacterial diversity emerged. The competitive stress for limited N may eliminate more bacteria from the communities than the increase of bacteria which are adapted to a lower-N environment.…”

Incorporating the effects of changes in vegetation functioning and CO 2 on water availability in plant habitat models

“…Higher CO 2 concentrations generally decrease stomatal conductance (Ainsworth & Long 2005), potentially leading to lower transpiration and increased soil water availability (Gerten et al 2005;Gedney et al 2006). On the other hand, vegetation productivity increases with CO 2 (Norby et al 2005), which may cause more transpiration through larger leaf areas (McCarthy et al 2006). Vegetation structure and functioning also respond to other drivers, such as longer growing seasons in the north (Lucht et al 2002;Morales et al 2007).…”