Houbao Fan

Linkages of plant and soil C:N:P stoichiometry and their relationships to forest growth in subtropical plantations

Background and aimsEcological stoichiometry plays important roles in ecosystem dynamics and functioning, but relationships between above- and belowground stoichiometry and stoichiometric effects on the growth of different plant functional groups in forests remain poorly understood.MethodsIn an age sequence of 2-, 4- and 6-year-old Eucalyptus plantations in subtropical China, we examined C, N and P concentrations and their ratios in the soil and leaves. Each plantation was divided into overstory and understory plant functional groups. The relationships between stoichiometric characteristics and forest growth were analyzed.ResultsSoil C and P decreased in the Eucalyptus age sequence, which led to changes in soil stoichiometric characteristics. Leaf C:P and N:P ratios were higher for Eucalyptus trees than for understory plants because of the low P concentrations in Eucalyptus leaves. Soil and plant N:P ratios were strongly related. Understory biomass was positively related to N:P ratios, while overstory growth was negatively related to N:P ratios.ConclusionsOur results suggest that nutrient concentrations in soil and plants are tightly linked in Eucalyptus plantations and that P limitation increases with stand age. Stoichiometric characteristics appear to mediate forest properties and functions under nutrient limitation in subtropical regions.

Asynchronous responses of soil microbial community and understory plant community to simulated nitrogen deposition in a subtropical forest

Atmospheric nitrogen (N) deposition greatly affects ecosystem processes and properties. However, few studies have simultaneously examined the responses of both the above- and belowground communities to N deposition. Here, we investigated the effects of 8 years of simulated N deposition on soil microbial communities and plant diversity in a subtropical forest. The quantities of experimental N added (g of N m−2 year−1) and treatment codes were 0 (N0, control), 6 (N1), 12 (N2), and 24 (N3). Phospholipid fatty acids (PLFAs) analysis was used to characterize the soil microbial community while plant diversity and coverage were determined in the permanent field plots. Microbial abundance was reduced by the N3 treatment, and plant species richness and coverage were reduced by both N2 and N3 treatments. Declines in plant species richness were associated with decreased abundance of arbuscular mycorrhizal fungi, increased bacterial stress index, and reduced soil pH. The plasticity of soil microbial community would be more related to the different responses among treatments when compared with plant community. These results indicate that long-term N deposition has greater effects on the understory plant community than on the soil microbial community and different conservation strategies should be considered.

Individual and interactive effects of drought and heat on leaf physiology of seedlings in an economically important crop

This study investigated the combined effect of drought and heat wave on physiological responses of tomato seedlings. We found that the negative impacts of drought stress were exacerbated by heat wave through stomatal and biochemical limitations. Additionally, the recovery of leaf gas exchange in the combination of drought and heat wave was delayed more than in other treatments. Our results suggest that future climates characterized by drought and extreme heat may have substantial impacts on tomato productivity and survival.

Individual size but not additional nitrogen regulates tree carbon sequestration in a subtropical forest

Recent studies have indicated that tree carbon accumulation in subtropical forests has been negatively affected by global change phenomena such as warming and drought. However, the long-term effect of nitrogen addition on plant carbon storage remains poorly understood in these regions. In this study, we conducted a 10-year field experiment examining the effect of experimental N addition on plant growth and carbon storage in a subtropical Chinese fir forest. The N levels were 0 (control), 60, 120, and 240 kg ha−1 yr−1, and the N effects on tree carbon were divided into stand and individual levels. The results indicated that tree carbon storage at the stand scale was not affected by long-term N addition in the subtropical forest. By contrast, significant impacts of different tree size classes on carbon sequestration were found under different N treatments, which indicated that the amount of plant carbon sequestration was significantly enhanced with tree size class. Our findings highlight the importance of community structure and growth characteristics in Chinese fir forests, in which individual size but not additional N regulates tree carbon sequestration in this subtropical forest.

Assessing bioaccessibility of Se and I in dual biofortified radish seedlings using simulated in vitro digestion

Selenium (Se) and iodine (I) are essential elements for humans, and biofortification of vegetables with these elements is an effective way to amend their deficiencies in the diet. In this study, the distribution and transformation of Se and I species were investigated in radish seedlings that were simultaneously supplemented with these two elements; the fate and the bioaccessibility of Se and I species were dynamically surveyed in the oral, gastric and intestinal phases using a simulated in vitro digestion method. The radish seedlings were cultivated in hydroponic conditions with Se (IV), Se (VI), I- and IO3- (each 1 mg L-1). The results revealed that Se-methylselenocysteine (MeSeCys), selenocystine (SeCys2), selenomethionine (SeMet) and Se (VI) were present in radish, and MeSeCys was the dominant species in both gastric and intestinal extracts, comprising 32.7 ± 1.5% and 39.6 ± 1.1% of the total content, respectively. I- was also the dominant species, which accounted for 57.1 ± 2.1%, 46.6 ± 1.5% and 68.8 ± 1.8% of the total digested content respectively in the oral, gastric and intestinal extracts. Meanwhile, IO3- was absent and organic I accounted for approximately 20%. The bioaccessibility of Se and I in the intestinal phase reached 95.5 ± 2.5% and 85.8 ± 0.9%, respectively; although after dialysis through membranes, the data reduced to 60.1 ± 2.8% and 39.6 ± 0.8%, respectively. Contents of MeSeCys and I- increased from the oral to intestinal phase and the bioaccessibility of both Se and I in radish was above 85%. So radish is suitable as a potential dietary source of Se and I with biofortification.

Estimations of evapotranspiration in an age sequence of Eucalyptus plantations in subtropical China

Eucalyptus species are widely planted for reforestation in subtropical China. However, the effects of Eucalyptus plantations on the regional water use remain poorly understood. In an age sequence of 2-, 4- and 6-year-old Eucalyptus plantations, the tree water use and soil evaporation were examined by linking model estimations and field observations. Results showed that annual evapotranspiration of each age sequence Eucalyptus plantations was 876.7, 944.1 and 1000.7 mm, respectively, accounting for 49.81%, 53.64% and 56.86% of the annual rainfall. In addition, annual soil evaporations of 2-, 4- and 6-year-old were 318.6, 336.1, and 248.7 mm of the respective Eucalyptus plantations. Our results demonstrated that Eucalyptus plantations would potentially reduce water availability due to high evapotranspiration in subtropical regions. Sustainable management strategies should be implemented to reduce water consumption in Eucalyptus plantations in the context of future climate change scenarios such as drought and warming.

Nutrient Accumulation and Cycling of an Eucalyptus urophylly×E. grandis Plantation

The nutrient accumulation and cycling were investigated from 2-to 6-year-old Eucalyptus urophylly × E.grandis plantations in the southern mountain region of Fujian Province,China.The results showed that N content was the highest in the tree components,followed by K,Ca,Mg and P.N content in the 2-,3-,4–year-old stands decreased,then increased slightly in the 5-and 6-year-old stands.The nutrient accumulations were 753.26,882.07,1 010.22,1 087.51,1 704.79 kg hm-2 in the 2-,3-,4-,5-and 6-year-old stands,respectively.Annual net nutrient accumulation was highest(505.36 kg hm-2) in the 6-yearold stand,and in the 2-,3-,4-,and 5-year-old stands,the values were 383.37,392.25,424.21,400.89 kg hm-1 a-1,respectively.The nutrient absorption increased along stand age while nutrient return showed a decreased trend.The coefficients of nutrient utilization were 0.51,0.44,0.42,0.37,0.30 along the forest age.The nutrient cycling coefficients did not show obvious trend with the values from 0.16 to 0.24.The recycling period of nutrients was 8.76,9.75,7.58,9.39,17.47 years along with stand age,respectively.The results indicate that Eucalyptus urophylly × E.grandis plantations have low nutrient utilization efficiency in the early stage while have high nutrient utilization efficiency.Nutrient deficient would limit biomass accumulation in these plantations and fertilization management should be considered.