Large-scale patterns of understory biomass and its allocation across China's forests.

Plant biomass storage and its allocation reflect the ecosystem productivity and adaptation to different environments. Understory vegetation is a significant component of any forest ecosystem and plays a vital role in biodiversity maintenance and the ecosystem's carbon cycle. Although many studies have addressed the relationships of climate, stand structure and resource availability with understory biomass and its allocation at local scales, the large-scale variation of understory biomass and allocation and their underlying mechanisms remain unclear. We compiled a large database of understory biomass at the community level across China's forests to explore the large-scale patterns of understory biomass and R/S ratio, and to quantify the relative importance of drivers. Understory biomass and R/S ratio varied largely with forest types, and decreased with increasing longitude, but increased with elevation. Understory biomass increased with increasing latitude, mean annual temperature (MAT), and mean annual precipitation (MAP), while the R/S ratio decreased with latitude, MAT, and MAP. Stand structure had a strong effect on the variations in understory biomass. MAP was the most important driver in determining R/S ratio. This synthesis provides a first assessment of the large-scale patterns of understory biomass and allocation and sheds new light on the mechanisms underlying the variations in understory biomass and its allocation over a broad geographic scale. These findings will improve predictions of understory community dynamics in response to climate change and aid in further optimizing ecosystem process models.

Carbohydrate dynamics of three dominant species in a Chinese savanna under precipitation exclusion.

The potential impact of drought on the carbon balance in plants has gained great attention. Non-structural carbohydrate (NSC) dynamics have been suggested as an important trait reflecting carbon balance under drought conditions. However, NSC dynamics under drought and the response mechanisms of NSC to drought remain unclear, especially in water-limited savanna ecosystems. A precipitation exclusion experiment was performed to simulate different drought intensities in a savanna ecosystem in Yuanjiang valley in southwestern China. Growth, total NSC concentration and diurnal change of NSC were determined for the leaves and non-photosynthetic organs of three dominant species (Lannea coromandelica, Polyalthia cerasoides and Heteropogon contortus) throughout the growing season. Drought significantly reduced the growth of all the three species. Total NSC concentration averaged ~8.1%, varying with species, organ and sampling period, and did not significantly decrease under drought stress. By contrast, the diurnal change of NSC in these three species increased under drought stress. These results indicate that these three dominant species did not undergo carbon limitation. Thus, relative change in NSC is a more sensitive and effective indicator than carbon reserves in evaluation of plant carbon balance. These findings provide new insights for the understanding of carbon balance and the mechanisms of carbon starvation.

Carbon exchanges and their responses to temperature and precipitation in forest ecosystems in Yunnan, Southwest China.

Forest ecosystems play an increasingly important role in the global carbon cycle. However, knowledge on carbon exchanges, their spatio-temporal patterns, and the extent of the key controls that affect carbon fluxes is lacking. In this study, we employed 29-site-years of eddy covariance data to observe the state, spatio-temporal variations and climate sensitivity of carbon fluxes (gross primary productivity (GPP), ecosystem respiration (Reco), and net ecosystem carbon exchange (NEE)) in four representative forest ecosystems in Yunnan. We found that 1) all four forest ecosystems were carbon sinks (the average NEE was -3.40tCha-1yr-1); 2) contrasting seasonality of the NEE among the ecosystems with a carbon sink mainly during the wet season in the Yuanjiang savanna ecosystem (YJ) but during the dry season in the Xishuangbanna tropical rainforest ecosystem (XSBN), besides an equivalent NEE uptake was observed during the wet/dry season in the Ailaoshan subtropical evergreen broad-leaved forest ecosystem (ALS) and Lijiang subalpine coniferous forest ecosystem (LJ); 3) as the GPP increased, the net ecosystem production (NEP) first increased and then decreased when the GPP>17.5tCha-1yr-1; 4) the precipitation determines the carbon sinks in the savanna ecosystem (e.g., YJ), while temperature did so in the tropical forest ecosystem (e.g., XSBN); 5) overall, under the circumstances of warming and decreased precipitation, the carbon sink might decrease in the YJ but maybe increase in the ALS and LJ, while future strength of the sink in the XSBN is somewhat uncertain. However, based on the redundancy analysis, the temperature and precipitation combined together explained 39.7%, 32.2%, 25.3%, and 29.6% of the variations in the NEE in the YJ, XSBN, ALS and LJ, respectively, which indicates that considerable changes in the NEE could not be explained by variations in the temperature and precipitation. Therefore, the effects of other factors (e.g., CO2 concentration, N/P deposition, aerosol and other variables) on the NEE still require extensive research and need to be considered seriously in carbon-cycle-models.

Eddy covariance and biometric measurements show that a savanna ecosystem in Southwest China is a carbon sink.

Savanna ecosystems play a crucial role in the global carbon cycle. However, there is a gap in our understanding of carbon fluxes in the savanna ecosystems of Southeast Asia. In this study, the eddy covariance technique (EC) and the biometric-based method (BM) were used to determine carbon exchange in a savanna ecosystem in Southwest China. The BM-based net ecosystem production (NEP) was 0.96 tC ha-1 yr-1. The EC-based estimates of the average annual gross primary productivity (GPP), ecosystem respiration (Reco), and net ecosystem carbon exchange (NEE) were 6.84, 5.54, and -1.30 tC ha-1 yr-1, respectively, from May 2013 to December 2015, indicating that this savanna ecosystem acted as an appreciable carbon sink. The ecosystem was more efficient during the wet season than the dry season, so that it represented a small carbon sink of 0.16 tC ha-1 yr-1 in the dry season and a considerable carbon sink of 1.14 tC ha-1 yr-1 in the wet season. However, it is noteworthy that the carbon sink capacity may decline in the future under rising temperatures and decreasing rainfall. Consequently, further studies should assess how environmental factors and climate change will influence carbon-water fluxes.

Disc swelling and mild initial visual acuity loss predict a better short-term visual acuity outcome in bilateral acute optic neuritis.

Bilateral acute optic neuritis (AON) is rare in adults in Western countries, but is relatively common in Asian populations. We aimed to document clinical features in Chinese patients with bilateral AON, and to identify factors that are predictive of visual acuity outcome. We reviewed 41 patients (23 males, 18 females; age 18-74 years) diagnosed with bilateral AON from three centers between 2003 and 2009. Demographic and clinical data were compared to a group of patients with unilateral AON. Univariate analysis and multivariate linear regression were used to identify prognostic factors. We found that the median visual acuity (expressed as the logarithm of the minimal angle of resolution [LogMAR] scores) in our patients was 1.55 at presentation and 0.72 at discharge (p<0.001). There was a higher proportion of males (56% compared to 34%, p=0.015), a higher percentage with disc swelling (71% compared to 48%, p=0.014), and poorer visual acuity at presentation (median LogMAR scores: 1.55 compared to 1.70, p=0.001) in patients with bilateral AON than in those with unilateral AON. Both disc swelling (p=0.036) and visual acuity at presentation (p=0.023) were significantly associated with visual acuity at discharge. Our study suggests that bilateral AON has some clinical differences to unilateral AON, and that disc swelling and initial visual acuity may predict a short-term visual acuity outcome in bilateral AON.

Unilateral optic neuritis in a Chinese population in three centers.

To describe the clinical profile of unilateral optic neuritis (ON) in a Chinese population, we reviewed retrospectively the records of 100 patients (66% female; age 18-74 years) diagnosed with unilateral ON between 2003 and 2009 at three hospitals in Guangxi Province, China. Ocular pain was noted in 40% and disc swelling in 48%. Periventricular plaques were found in 8% and multiple sclerosis in 6%. Visual loss varied at presentation, being mild (≥ 0.5) in 15%, moderate (0.1-0.4) in 26%, and severe (< 0.1) in 59%. Visual acuity improved after a mean (± standard deviation) hospitalization of 12.5 ± 5.3 days, with visual loss eing mild in 52%, moderate in 14% and severe in 34%. Our findings suggest that the characteristics and severity of initial visual loss of patients in our study are more similar to those of patients in Japan than to those of patients in the United States of America. It seems that visual recovery in our patients is relatively good.