Effects of freeze damage on litter production, quality and decomposition in a loblolly pine forest in central China

Background and aims

Freeze events can strongly influence many ecosystem processes. However, the effects of freeze events on litter production, litter quality, and decomposition are rarely documented.

Methods

In this study, litter fall was measured monthly for 2 years. Two litter decomposition experiments were also performed using freeze-damaged litter and non-damaged litter in a loblolly pine forest.

Results

The freeze event in November 2009 caused a pronounced pulse of needle litter fall. The freeze-damaged needle litter was shown to have higher N concentration and lower C/N ratio compared with the normal falling needle litter. This finding indicates that freeze damage significantly increased needle quality because of incomplete nutrient resorption. The decomposition of freeze-damaged needle litter was faster than that of normal falling yellow needle litter and slower than that of hand-picked green needle litter. The decomposition rate constant (k) was negatively correlated with the C/N ratio in the needle litter. Our results also showed that the different climatic conditions influence patterns of litter decomposition.

Conclusions

This study suggests that freeze events significantly alter litter quantity and quality, thus affecting litter decomposition rates in a loblolly pine forest in central China.     

Identification and Analysis of Resistance‐like Genes in the Tomato Genome

Tomato (Solanum lycopersicum L.) is one of the most important vegetable crops in the world. However, the tomato production is severely affected by many diseases. The use of host resistance is believed to be the most effective approach to control the pathogens. In this study, a total of 1003 resistance‐like genes were identified from the tomato genome using individual full‐length search and conserved domain verification approach. Of the predicted resistance genes, serine/threonine protein kinase was the largest class with 384 genes followed by 212 genes encoding receptor‐like kinase, 107 genes encoding receptor‐like proteins, 68 genes encoding coiled‐coil–nucleotide‐binding site (NBS)–leucine‐rich repeat (LRR) and 19 genes encoding Toll interleukin‐1 receptor domain‐NBS‐LRR. Physical map positions established for all predicted genes using the tomato WGS chromosomes SL2.40 information indicated that most resistance‐like genes clustered on certain chromosomal regions. Comparisons of the sequences from the same resistance‐like genes in S. pimpinellifolium and S. lycopersicum showed that 93.5% genes contained single nucleotide polymorphisms and 19.7% genes contained insertion/deletion. The data obtained here will facilitate isolation and characterization of new resistance genes as well as marker‐assisted selection for disease resistance breeding in tomato.     

The Preliminary Study of 16α-[18F]fluoroestradiol PET/CT in Assisting the Individualized Treatment Decisions of Breast Cancer Patients

Objective

To evaluate the clinical value of 16α-[18F]fluoroestradiol (18F-FES) PET/CT in assisting the individualized treatment decisions of breast cancer patients.

Methods

Thirty-three breast cancer patients, who underwent both 18F-FES and 18F-FDG PET/CT from July 2010 to March 2013 in our center, were enrolled in this preliminary study. All the patients used 18F-FES PET/CT as a diagnostic tool with a clinical dilemma. We used the maximum Standardized Uptake Value (SUVmax) to quantify ER expression and a cutoff value of 1.5 to dichotomize results into ER positive and negative lesions. All patients were clinically followed up at least 6 months.

Results

In evaluating equivocal lesions on conventional work-up group (n = 4), three lung lesions and another iliac lesion were enrolled. As for three lung lesions, 18F-FES PET/CT showed one lesion with high uptake, which suggested it was an ER positive metastasis. The other two lesions were 18F-FES negative, which meant an ER negative metastasis or secondary primary tumor. Additionally, one iliac lesion was detected by MRI. 18F-FDG uptake was high at the suspected lesion, whereas 18F-FES uptake was absent; In predicting origin of metastasis group (n = 2), two breast cancer patients had secondary primary tumors were collected. They were 18F-FES negative, which showed low possibility of metastasis from breast cancer and they were all confirmed by biopsy. In detecting ER status in metastasis group (n = 27), 18F-FES PET/CT showed increased 18F-FES uptake in all metastatic lesions in 11 patients; absent in all lesions in 13 patients; and the remaining 3 patients had both 18F-FES positive and negative lesions. Totally, on the basis of the 18F-FES PET/CT results, we found changes in the treatment plans in 16 patients (48.5%, 16/33).

Conclusions

18F-FES PET/CT could assess the entire tumor volume receptor status; therefore, it may be used to assist the individualized treatment decisions of breast cancer patients.     

不同人工林生态系统林地土壤质量评价

利用定位研究方法,综合比较了第2代连栽杉木纯林、杉木与阔叶树混交林以及阔叶纯林3种人工林生态系统对林地土壤质量的影响.结果表明,与连栽杉木纯林相比,在杉阔混交和阔叶树轮栽两种经营模式下,土壤养分含量增加,物理性状改善,土壤生物活性提高.利用土壤质量评价体系在对土壤功能评价的基础上,直观评价了3种经营模式的土壤质量状况.在研究区内,杉木与阔叶树混交以及阔叶树轮栽的水分有效性、养分有效性和根系适宜性以及最终的土壤质量指数均处于中等水平,而连栽杉木林的水分有效性、养分有效性和根系适宜性较差,土壤质量指数处于较低水平.总有机C、阳离子交换量和微生物生物量C与其它土壤理化性质和生物学性质之间明显相关,可将其作为研究区土壤质量的指示指标;土壤微生物生物量C、N、P与土壤总有机C、土壤全N、土壤全P含量之间也存在较好的相关性.     

凋落物化学组成对土壤微生物学性状及土壤酶活性的影响

通过模拟试验的方法研究了单一施加杉木(Cunn inghan ia lancceola ta(L am b)Hook.)叶凋落物,杉木(C.lancceola ta)和桤木(A lnus crem astogyne Burk ill)混合凋落物,杉木(C.lancceola ta)和枫香(L iqu id am ba f orm osana H ance)混合凋落物,杉木(C.lancceola ta)、桤木(A.crem astogyne)、枫香(L.f orm osana)混合凋落物对土壤化学性状和土壤微生物量碳、代谢熵(qCO2)、土壤酶活性的影响。研究结果表明,土壤微生物学性状比土壤化学性状对不同凋落物处理的效应反应更敏感;与单一杉木叶凋落物比较,混合凋落物处理的土壤微生物量碳明显增加,土壤脲酶、蔗糖酶、脱氢酶活性升高;土壤代谢熵(qCO2)和土壤多酚氧化酶活性有下降趋势;另外,研究结果也表明,不同树种的叶凋落物混合对土壤质量的影响存在差异,有桤木叶的混合凋落物对土壤质量的改善效果似乎更明显。     

杉木人工林取代天然次生阔叶林对土壤生物活性的影响

对我国亚热带南、中、北3个区带杉木人工林与天然次生阔叶林表层土壤化学性状、土壤生物活性特征进行研究.结果表明,杉木人工林取代天然次生林阔叶林后表层土壤总有机碳含量下降31.51%～58.24%,土壤全氮、全磷、pH值以及土壤C/N、C/P比亦呈下降趋势;杉木人工林取代天然次生阔叶林后表层土壤细菌、真菌数量减少;土壤脲酶、蔗糖酶、过氧化氢酶和脱氢酶活性下降,而土壤多酚氧化酶活性增加8%～40%;杉木人工林与天然次生林阔叶林相比,土壤呼吸强度下降51.15%～54.48%.相关分析发现,土壤总有机碳与土壤多酚氧化酶活性呈负相关(R=-0.723,n=18),与土壤全氮、全磷及其它土壤酶活性呈正相关.杉木人工林取代天然次生林阔叶林使林内表层土壤质量恶化.杉木人工林土壤有机质丢失是导致杉木人工林土壤养分减少、土壤生物活性下降的重要原因.     

杉木人工林土壤质量演变过程中土壤微生物群落结构变化

以中国科学院会同森林生态站自然林、杉木连栽林和杉木阔叶树混交林地土壤为研究对象,采用PCR-DGGE、DNA-sequencing和主成分分析(PCA)等方法分析土壤微生物群落结构变化及其与土壤质量变化之间的关系.结果表明,该地区杉木人工林土壤中细菌优势种群为α-、β-、γ-proteobacteria和Cytophaga-Flexibacter-Bacterioides (CFB)类群;真菌优势种群为子囊菌(Ascomycetes)和担子菌(Basidiomycetes)亚门的种属.杉木人工林替代自然林后,土壤细菌多样性指数显著降低,且随连栽代数增加呈持续降低趋势;杉木人工林土壤中与Pedobacter cryoconitis亲缘关系密切的细菌种群消失,出现与Xanthomonas sp.和Rhodanobacter sp.亲缘关系密切的细菌种群.土壤真菌群落结构的变化与细菌相反,杉木人工林替代自然林后并不断连栽时,土壤真菌多样性指数呈现上升的趋势,自然林土壤中优势真菌种群在杉木三代林中消失.杉木与火力楠或桤木混交后土壤细菌和真菌种群结构与自然林类似.土壤细菌多样性指数与土壤总有机碳、全氮、可溶性有机碳、铵态氮、速效磷、速效钾含量以及土壤pH值呈显著正相关关系(P＜0.05).土壤真菌多样性指数仅与土壤碳氮比呈显著正相关关系,而与土壤pH值呈显著负相关关系.杉木林土壤质量变化对土壤细菌和真菌优势种群有较大影响,细菌Burkholderia sp.、Pedobactersp.、Xanthomonas sp.和真菌Sclerotinia sclerotiorum、Mycosphaerella cannabis可能是引起土壤质量变化的关键种群.     

杉木、火力楠纯林及其混交林生态系统C、N贮量

研究比较第2代连载杉木纯林、杉木与火力楠混交林以及火力楠纯林3种人工林生态系统的C、N贮量。结果表明,杉木与火力楠混交林生态系统C贮量要高于杉木纯林和火力楠纯林,而生态系统N贮量是火力楠纯林和杉木与火力楠混交林高于杉木纯林;生态系统C和N贮量的空间分布基本一致,土壤层占主要部分,其次为乔木层,再次是根系,林下植被层和凋落层所占比例最小;相关分析表明,土壤C、N贮量分别和林下植被生物量以及与森林凋落物现存量之间都具有良好的线性关系,说明林下植被和森林凋落物对土壤C、N贮量有着深刻的影响。