Leaf Caloric Value from Tropical to Cold-Temperate Forests: Latitudinal Patterns and Linkage to Productivity.

Leaf caloric value (LCV) reflects the capacity of a leaf to fix and accumulate solar energy through photosynthesis. We systematically investigated the LCV of 745 plant species in 9 forests, representing a range of tropical to cold-temperate forests along the 4700-km North-South Transect of Eastern China. The goals were to explore the latitudinal patterns of LCV at the levels of species, plant functional group, and community and to establish the relationship between LCV and gross primary productivity (GPP). Our results showed that LCV for all species ranged from 12.85 to 22.15 KJ g-1 with an average of 18.46 KJ g-1. Plant functional groups had a significant influence on LCV, with trees > shrubs > herbs, conifers > broadleaved trees, and evergreens > deciduous trees. The different values of LCV represented the long-term evolution and adaptation of plant species to different environments. Unexpectedly, no apparent latitudinal trends of LCV at community level were observed, although LCV at the species level clearly decreased with increasing latitude. Use efficiency of LCV (CUE, gC KJ-1), defined as the ratio of GPP to total LCV at the community level, varied quadratic with latitude and was lower in the middle latitudes. Climate (temperature and precipitation) may explain 52.9% of the variation in spatial patterns of CUE, which was positively correlated with aridity. Our findings are the first large-scale report of the latitudinal patterns of LCV in forests at the species, plant functional group, and community levels and provide new insights into the relationship between LCV and ecosystem functions in forest communities

Asynchronous pulse responses of soil carbon and nitrogen mineralization to rewetting events at a short-term: Regulation by microbes

Rewetting after precipitation events plays an important role in regulating soil carbon (C) and nitrogen (N) turnover processes in arid and semiarid ecosystems. Here, we conducted a 48-h rewetting simulation experiment with measurements of soil C and N mineralization rates (R-C and R-N, respectively) and microbial biomass N (MBN) at high temporal resolution to explore the pulse responses of R-C and R-N. R-C and R-N responded strongly and rapidly to rewetting over the short term. The maximum RC value (because of pulse effects) ranged from 16.53 to 19.33 mu g C g(soil)(-1) h(-1), observed 10 min after rewetting. The maximum RN varied from 22.86 to 40.87 mu g N g(soil)(-1) h(-1), appearing 5-6 h after rewetting. The responses of soil microbial growth to rewetting were rapid, and the maximum MBN was observed 2-3 h after rewetting. Unexpectedly, there was no correlation between R-C, R-N, and MBN during the process of rewetting, and R-C and R-N were uncoupled. In sum, the pulse responses of R-C, R-N, and microbial growth to simulated rewetting were rapid, strong, and asynchronous, which offers insights into the different responses of microbes to rewetting and mechanisms behind microbes

Changes in leaf caloric value among different types of trees in Chinese forests.

<p>Panel A, C and B, D were calculated at each site and for the total transect, respectively. Data are represented as mean ± S.E. Different letters indicate a significant difference among plant functional types (<i>p</i> < 0.05).</p

Frequency distribution of leaf caloric values in Chinese forests.

<p>Frequency distribution of leaf caloric values in Chinese forests.</p

Changes in leaf caloric value among different plant functional groups.

<p>LCV_T, LCVs, and LCV_H, are the average of leaf caloric values weighted for the relative leaf biomass of trees, shrubs, and herbs, respectively. LCV_T, LCVs, and LCV_H, the average of leaf caloric values weighted for the relative leaf biomass of trees, shrubs, and herbs, respectively. HZ, Huzhong; LS, Liangshui; CB, Changbai; DL, Dongling; TY, Taiyue; SN, Shennongjia; JL, Jiulian; DH, Dinghu; JF, Jianfengling. Panel A and B were calculated at each site and for the total transect, respectively. Data are represented as mean ± S.E. Different letters indicate a significant difference among plant functional types (<i>p</i> < 0.05).</p

Description of the study sites.

<p>Description of the study sites.</p