Interactions between Two Fungi Strains during Litter Decomposition through a Microcosm Experiment: Different Degradative Enzyme Activities

Fungi are the key agents in litter decomposition in forest ecosystems. However, the specific roles of the interactions between different fungal species during litter decomposition process are unclear. To evaluate the interactions, two fungi strains with significantly different morphs were isolated from the soils of Quercus acutissima forest and Pinus massoniana forest, and inoculated in the litter powder of Quercus acutissima leaves and Pinus massoniana needles with grown separately and in coexistence equally through a microcosm experiment. The enzyme activities were determined as a proxy for microbial activities. The results showed that the degradative enzymes involved in litter decomposition showed varying dynamics pattern during the incubation period. The interactions between the two fungi strains are synergism, and benefit to each other according to enzyme activities, suggesting that a fungi strain growth was accelerated by the presence of other fungi strain during litter decomposition process. However, the interactions of the two fungi strains were bilateral antagonism inoculated in the litter powder of Quercus acutissima leaves according to cellobiohydrolase activities. The synergism, despite bilateral antagonism in an exceptional case, may be an important factor controlling the fungal colonization and growth on litter substrate. The results implied that more fungal species may accelerate litter decomposition rates due to their mutual cooperation.

Productivity and the Survival Rate after Winter Management of Seven Tropical Forage Accessions in Subtropical Region of China

Forage production and quality of five tropical grass accessions (Guimu-1 hybrid elephant grass (PG1), Mulato II (M II), Ubon paspalum (PU), hybrid elephant grass (PH) and Reyan 11 paspalum (PR11)) and two tropical legume accessions (Reyan 5 stylo (SR5) and Ubon stylo (SU)) were evaluated in a field experiment in a subtropical area with hot summers and cold winters in Guangxi, China. Three forage stubble cover managements: no cover (CK), dry mass cover (MC) and plastic cover (PC) were applied at the end of the summer period to evaluate cold tolerance and accession survival over the winter. Photosynthesis measurements were taken from the forages in mid-summer. The results showed that PG1 accession produced significantly higher dry matter yields (67.0 t·ha-1) than the other grass and legume accessions. Legume accessions SU and SR5 produced much less dry matter (6.4 - 7.2 t·ha-1) compared to the grasses. M II, PU and PR11 contained the largest proportion of leaf. PG1 and PH showed good cold tolerance (survival rate >85%) under -1°C conditions without any cover management. PR11 had better cold tolerance than PU. M II exhibited very poor winter survival under no cover and with massive cover, and only survived well under plastic cover. The two stylo accessions died completely under all winter cover management treatments. In the growing season, under a given photosynthesis photon flux density (PPFD) = 1500 μmol m-2 s-1, the net photosynthesis rate Pn of all the seven accessions was above 28 μmol m-2 s-1, of which hybrid elephant grass and M II were above 42 μmol m-2 s-1. Though these 7 tropical accessions yielded high production in the grow season, stylo and M II are sensitive to cold in subtropical region of Guangxi. The result suggests that PG1 and PU are good accessions and can be used as productive perennial pasture, while stylo and M II are simply considered as annual one. Additionally, if paspalum was trained in cool region before being introduced to subtropical region, it may present both productivity and enhancive cold tolerance.

Effects of Thallium Stress on Photosynthesis, Chlorophyll Fluorescence Parameters and Antioxidant Enzymes Activities of Coix Lacryma-jobi

Levels of T1 （Thallium） in soil from 0 （control） to 50 μg/L through 0.2, 0.5, 1 and 2.5μg/L were directly and positively correlated to levels of T1 in plant tissue, the accumulation being maximum in roots, intermediate in leaves and minimum in stems. Thallium, especially at higher concentrations, adversely affected photosynthesis （as judged based on chlorophyll fluorescence parameters）, suggesting inhibition of photo-activation of PSII （Photosystems II）, and also decreased the rate of photosynthesis, the rate of transpiration and stomatal conductivity drastically. Exposure to TI also increased the activity of CAT （Catalase） （except at 1 μg/L） and POD （Peroxidase） （except at 0.2 μg/L）, suggesting that the antioxidant systems in Coix lacryma-jobi were the main contributors of CAT and SOD （Superoxide Dismutase） and that the tolerance of C. lacryma-jobi to T1 is mainly due to this induced antioxidant machinery.

Adaptation of microbial communities to multiple stressors associated with litter decomposition of Pterocarya stenoptera

To understand the further impacts of multiple stressors in freshwater, we investigated the effects of heavy metal （HM, Cu and Zn） and nutrient enrichments （nitrogen and phosphorus, NP） on microbial decomposition of Pterocarya stenoptera litter and the associated extracellular enzyme activities and microbial biomass with microcosms. Results showed that the decomposition rates were slower in the polluted stream waters than those in the unpolluted ones, which corresponded to lower microbial biomass and integrated enzyme activities of cellulose and ^-glucosidase. The decomposition rates were accelerated at low HM level, which was associated with the stimulated enzyme activities of hydrolytic enzymes or was stimulated by both NP levels in polluted stream waters. In particular, the hydrolase enzyme activities of microbial communities in polluted stream waters were stimulated by low HM level, suggesting that low HM level-stimulated litter decomposition may be due to the increased enzymatic activities. When microbial communities were exposed to HM and NP simultaneously, the inhibitory effect （in unpolluted stream waters） or the stimulated effect （in polluted stream waters） of low HM concentration was enhanced and attenuated, respectively, which suggests that the NP antagonistic effect against HM toxicity on litter decomposition may contribute to the litter- associated extracellular enzyme activities. These results suggest that the may have antagonistic effects on stream ecosystem functioning. of HM and NP