Both increasing frequency of drought and drought duration are expected for many terrestrial ecosystems under on-going climate change. However, our understanding of the drought effect on soil ...respiration (Rs), which comprises the second largest carbon (C) flux of the global C cycle, remains limited. To explore the effects of reduced precipitation on Rs and its components, we conducted an experiment of throughfall rainfall exclusion during two consecutive growing seasons in a subtropical forest in the Southeast China. Following throughfall exclusion Rs declined rapidly, and did not recover until three to four months following rewetting, in both 2014 and 2015. During the experiment, throughfall exclusion significantly reduced autotrophic soil respiration (Ra); however, heterotrophic soil respiration (Rh) was unaffected, resulting in a reduced contribution (Ra/Rs) from 33 ± 1% for the control to 16 ± 3% under throughfall exclusion. Experimental drought significantly reduced soil microbial C and fine root biomass, and subsequent to rewetting, soil microbial C recovered quickly, but fine root biomass relapsed slowly. Our results suggested that prolonged drought decreases Rs through modifications in soil microbial activities and fine root metabolic capacity, which are induced by reduced soil water availability. Moreover, our results imply that drought-induced reductions in Rs originate primarily from Ra. Our results highlight the need to account for asymmetric responses to drought between Ra and Rh when predicting the reaction of the ecosystem C balance in response to future drought events.
•Prolonged drought sharply decreased Rs and temperature sensitivity Q10.•The negative effects of droughts were more pronounced in Ra than Rh.•The weak response of Rs was discovered subsequent to rewetting.•The reduction of drought-induced Rs originated primarily from Ra.•The decrease in Rs was related to modifications in soil microbe and fine root activities.
In this study, we investigated the effects of environmental factors on plant phenolic variability, seasonal dynamics of total phenolic content (TP), extractable condensed tannins (ECT), protein-bound ...condensed tannins (PBCT), fiber-bound condensed tannins (FBCT), total condensed tannins (TCT), protein precipitation capacity (PPC) and nutrient content in the branchlets and fine roots of
Casuarina equisetifolia
. TP and TCT concentrations in branchlets were lowest in the spring, then increased in summer and autumn, similar to the seasonal dynamics in air temperature. TP and TCT concentrations in fine roots were highest in summer, coinciding with heavy precipitation. In general, TP and TCT concentrations were higher in branchlets than in fine roots. No significant difference was found in C concentration among various seasons for either branchlets or fine roots. Branchlets had significantly higher N and P concentrations than fine roots in most seasons. The C/N and N/P ratios in branchlets were significantly lower than in fine roots in all seasons, except summer. The relationship between branchlets and fine roots was significant for C, P and FBCT, but no significant relationships were found for N, TP, ECT, PBCT and TCT. Additionally, TP and TCT content were each significantly correlated with PPC in branchlets and in fine roots. Both TP/N and TCT/N ratios were highest in the autumn for the branchlets and in the summer for fine roots. The results indicate that high temperatures lead to increased tannin production in branchlets, but that the tannin content in fine roots is mainly affected by precipitation. Tannin content was greater in branchlets than in fine roots, which may indicate that selective pressure is greater on branchlets than on fine roots.
Casuarina equisetifolia (L.) is an indispensable tree species in the construction of the backbone of the shelterbelt system in subtropical coastal regions, as it can resist wind, sand, drought, and ...salt. Under global warming and water shortage, it is important to clarify the mechanisms through which C. equisetifolia adapts to drought stress and to breed drought-resistant varieties in order to enhance the ecological protection provided by coastal shelterbelts. Here, we aimed to explore the response characteristics of C. equisetifolia to drought stress and investigate the associations of NAC genes with drought resistance. Seedlings of 16 half-sib C. equisetifolia families were subjected to drought treatment. Seedling growth, morphology, physiological and biochemical indices, and drought resistance were comprehensively evaluated. The drought-resistant families designated 4-383, 3-80, 3-265, 3-224, and 1-195 were selected using multiple indices and methods. Correlation and structural equation model analyses revealed that CCG007578 might regulate growth and osmoprotection in C. equisetifolia while CCG028838 and CCG004029 may scavenge reactive oxygen species. The correlation and structural equation model analyses of seedling height growth (ΔH), survival rate (S), malondialdehyde (MDA), superoxide dismutase (SOD), and CCG007578 expression were used to identify drought resistance in C. equisetifolia. The aforementioned drought-resistant families provide basic materials for future research on genes encoding drought-resistance proteins and the molecular breeding of drought-resistant C. equisetifolia.
Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil ...respiration (
R
s
) for secondary natural Litsea forest and plantations of casuarina, pine, acacia and eucalyptus. Results show that significant diurnal variations of
R
s
occurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of
R
s
were found in all five forest stands.
R
s
changed exponentially with soil temperatures at the 10-cm depth; the models explain 43.3–77.0% of
R
s
variations. Positive relationships between seasonal
R
s
and soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter (
Q
10
value) of
R
s
ranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual
R
s
was highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter, and soil properties (pH, total N, available P, and exchangeable Mg) were also significant factors.
The rates of carbon bio‐sequestration within silica phytoliths of the leaf litter of 10 economically important bamboo species indicates that (a) there is considerable variation in the content of ...carbon occluded within the phytoliths (PhytOC) of the leaves between different bamboo species, (b) this variation does not appear to be directly related to the quantity of silica in the plant but rather the efficiency of carbon encapsulation by the silica. The PhytOC content of the species under the experimental conditions ranged from 1.6% to 4% of the leaf silica weight. The potential phytolith carbon bio‐sequestration rates in the leaf‐litter component for the bamboos ranged up to 0.7 tonnes of carbon dioxide (CO2) equivalents (t‐e‐CO2) ha−1 yr−1 for these species. Assuming a median phytolith carbon bio‐sequestration yield of 0.36 t‐e‐CO2 ha−1 yr−1, the global potential for bio‐sequestration via phytolith carbon (from bamboo and/or other similar grass crops) is estimated to be ∼1.5 billion t‐e‐CO2 yr−1, equivalent to 11% of the current increase in atmospheric CO2. The data indicate that the management of vegetation such as bamboo forests to maximize the production of PhytOC has the potential to result in considerable quantities of securely bio‐sequestered carbon.
Acacia crassicarpa (Fabaceae), a nitrogen-fixing tree species, is critically important for coastal protection in southeast China. In this study, we report the complete chloroplast genome sequence of ...A. crassicarpa, with a length of 176,493 bp. It contains a pair of inverted repeats (IR 39,851 bp), a large single-copy region (LSC 91,869 bp), and a small single-copy region (SSC 4,922 bp). The complete genome comprises 138 genes, including 93 protein-coding genes, 37 tRNA, and 8 rRNA genes. Our phylogenetic analysis reveals that A. crassicarpa is closely related to A. podalyriifolia and A. dealbata.
Soil CO2 flux to the atmosphere is a major factor affecting the global carbon cycle. The CO2 flux between soil layers is driven by soil temperature,moisture,and substrate supply. Soil CO2 flux and ...its major driving factors vary temporally and spatially within soil profiles. However,many studies have focused only on the surface soil,which is insufficient to correctly clarify the actual soil CO2 release processes,because soil CO2 flux is the addition of CO2 production in each soil layer under different biological,chemical,and physical conditions. The vertical distribution of soil CO2 flux should be considered to better understand the production processes in soil CO2. Moreover,in the next few decades,an increasing frequency and duration of droughts is expected in subtropical regions in China as a result of global climatechange. However,our understanding of the effect of drought on the vertical partitioning of soil CO2 flux is not well known. In the present study,a throughfall exclusion experiment was established
Xiamen is an economically competitive and highly urbanized city along the coastal area of Fujian Province, China. The research on spatio-temporal variation of landscape heterogeneity under the ...influence of human activities is of great importance to the further study on the relationship of landscape pattern and ecological process. It is also crucial to the discovery of spatial variation and intensity distribution of human activities. The research analyzed the intensity of human impacts and the spatial variation features and dynamics of landscape patterns by introducing statistical theories and approaches. We analyzed spatio-temporal variation of landscape heterogeneity using the geostatistical techniques, such as semivariogram and Kriging interpolation. Results show that there is a higher correlation between landscape heterogeneity indexes and human impact index. Both the indexes show a moderate spatial autocorrelation as well as an obvious characteristic of anisotropy. From 1998 to 2008, the spatial differentiation of the changes in the intensity of human activities and the changes in landscape heterogeneity shows that the landscape patterns in Xiamen are closely related with the urban land utilization methods, the condition of traffic and geographical location and the physical geographical condition such as the terrain and the ecological environment. The process of urbanization has a significant impact on the urban landscape pattern.
Summary
Casuarina equisetifolia (C. equisetifolia), a conifer‐like angiosperm with resistance to typhoon and stress tolerance, is mainly cultivated in the coastal areas of Australasia. ...C. equisetifolia, making it a valuable model to study secondary growth associated genes and stress‐tolerance traits. However, the genome sequence is unavailable and therefore wood‐associated growth rate and stress resistance at the molecular level is largely unexplored. We therefore constructed a high‐quality draft genome sequence of C. equisetifolia by a combination of Illumina second‐generation sequencing reads and Pacific Biosciences single‐molecule real‐time (SMRT) long reads to advance the investigation of this species. Here, we report the genome assembly, which contains approximately 300 megabases (Mb) and scaffold size of N50 is 1.06 Mb. Additionally, gene annotation, assisted by a combination of prediction and RNA‐seq data, generated 29 827 annotated protein‐coding genes and 1983 non‐coding genes, respectively. Furthermore, we found that the total number of repetitive sequences account for one‐third of the genome assembly. Here we also construct the genome‐wide map of DNA modification, such as two novel forms N6‐adenine (6mA) and N4‐methylcytosine (4mC) at the level of single‐nucleotide resolution using single‐molecule real‐time (SMRT) sequencing. Interestingly, we found that 17% of 6mA modification genes and 15% of 4mC modification genes also included alternative splicing events. Finally, we investigated cellulose, hemicellulose, and lignin‐related genes, which were associated with secondary growth and contained different DNA modifications. The high‐quality genome sequence and annotation of C. equisetifolia in this study provide a valuable resource to strengthen our understanding of the diverse traits of trees.
Significance Statement
We constructed a high‐quality draft genome sequence of C. equisetifolia and systematically characterized 29,827 annotated protein‐coding genes and 1,983 non‐coding genes, respectively. Furthermore, we construct the genome‐wide map of DNA modification, such as two novel forms N6‐Adenine (6mA) and N4‐methylcytosine (4mC), including the genes in the regulation of lignin and cellulose. The high‐quality genome resource in this study provides valuable resources to strengthen our understanding of the diverse traits of trees.
Casuarina equisetifolia (L.) is an indispensable tree species in the construction of the backbone of the shelterbelt system in subtropical coastal regions, as it can resist wind, sand, drought, and ...salt. Under global warming and water shortage, it is important to clarify the mechanisms through which C. equisetifolia adapts to drought stress and to breed drought-resistant varieties in order to enhance the ecological protection provided by coastal shelterbelts. Here, we aimed to explore the response characteristics of C. equisetifolia to drought stress and investigate the associations of NAC genes with drought resistance. Seedlings of 16 half-sib C. equisetifolia families were subjected to drought treatment. Seedling growth, morphology, physiological and biochemical indices, and drought resistance were comprehensively evaluated. The drought-resistant families designated 4-383, 3-80, 3-265, 3-224, and 1-195 were selected using multiple indices and methods. Correlation and structural equation model analyses revealed that CCG007578 might regulate growth and osmoprotection in C. equisetifolia while CCG028838 and CCG004029 may scavenge reactive oxygen species. The correlation and structural equation model analyses of seedling height growth (ΔH), survival rate (S), malondialdehyde (MDA), superoxide dismutase (SOD), and CCG007578 expression were used to identify drought resistance in C. equisetifolia. The aforementioned drought-resistant families provide basic materials for future research on genes encoding drought-resistance proteins and the molecular breeding of drought-resistant C. equisetifolia.
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