Plant-soil feedback regulates the trade-off between phosphorus acquisition pathways in Pinus elliottii.

Plant-soil feedback (PSF) is conventionally characterized by plant biomass growth, yet it remains unclear how PSF affects plant nutrient acquisition strategies (e.g., nutrient absorption and nutrient resorption) associated with plant growth, particularly under changing soil environments. A greenhouse experiment was performed with seedlings of Pinus elliottii Englem and conditioned soils of monoculture plantations (P. elliottii and Cunninghamia lanceolata Hook). Soil sterilization was designed to test plant phosphorus (P) acquisition strategy with and without native soil fungal communities. Soils from P. elliottii and C. lanceolata plantations were used to explore the specific soil legacy effects on two different P acquisition pathways (absorption and resorption). Phosphorus addition was also applied to examine the separate and combined effects of soil abiotic factors and soil fungal factors on P acquisition pathways. Due to diminished mycorrhizal symbiosis, PSF prompted plants to increasingly rely on P resorption under soil sterilization. In contrast, P absorption was employed preferentially in the heterospecific soil, where species-specific pathogenic fungi could not affect P absorption. Higher soil P availability diluted the effects of soil fungal factors on the trade-off between the two P acquisition pathways in terms of the absolute PSF. Moreover, P addition plays a limited role in terms of the relative PSF and does not affect the direction and strength of relative PSF. Our results reveal the role of PSF in regulating plant P acquisition pathways and highlight the interaction between mycorrhizal and pathogenic fungi as the underlying mechanism of PSF.

Contrasting effects of nitrogen and phosphorus additions on nitrogen competition between coniferous and broadleaf seedlings.

Nitrogen (N) is a major element limiting plant growth and metabolism. Nitrogen addition can influence plant growth, N uptake, and species interactions, while phosphorus (P) addition may affect N acquisition. However, knowledge of how nutrient availability influences N uptake and species interactions remains limited and controversial. Here, pot experiments were conducted for 14 months, in which conifers (Pinus massoniana and Pinus elliottii) and broadleaved trees (Michelia maudiae and Schima superba) were planted in monoculture or mixture, and provided additional N and P in a full-factorial design. Nitrogen addition increased the biomass, but P addition did not significantly affect the biomass of the four subtropical species. Combined N and P (NP) addition had no additive effect on plant biomass over N addition. Total plant biomass was significantly positively correlated to root traits (branching intensity and root tissue density) and leaf traits (net photosynthetic rate, stomatal conductance, and transpiration rate), but negatively correlated to root diameter in response to nutrient addition. Plant uptake rates of NH4+ or NO3- were not altered by N addition, but P or NP additions decreased NH4+ uptake rates and increased NO3- uptake rates. Neighboring conifers significantly inhibited NH4+ and NO3- uptake rates of the two broadleaf species, but neighboring broadleaves had no effects on the N uptake rates of pine species. The effects of nutrient additions on interspecific interactions differed among species. Nitrogen addition altered the interaction of P. elliottii and M. maudiae from neutral to competition, while P addition altered the interaction of P. massoniana and M. maudiae from neutral to favorable effects. Increasing nutrient availability switched the direction of interspecific interaction in favor of pines. This study provides insights into forest management for productivity improvement and optimizing the selection of broadleaf species regarding differences in soil fertility of subtropical plantations.

[Short-term responses of foliar multi-element stoichiometry and nutrient resorption of slash pine to N addition in subtropical China]. / äºšçƒ­å¸¦æ¹¿åœ°æ¾å¶ç‰‡å¤šå ƒç´ åŒ–å­¦è®¡é‡ä¸Žå »åˆ†å›žæ”¶å¯¹æ°®æ·»åŠ çš„çŸ­æœŸå“åº”.

We conducted a field experiment with three levels of N addition (0, 40 and 120 kg N·hm-2·a-1) in a Pinus elliottii plantation in subtropical China and collected green and senesced needles of P. elliottii at the peak (July) and the end (October) of each growing season in 2014 and 2015 for clarifying effects of nitrogen additions on concentrations of nine elements (C, N, P, K, Ca, Mg, Al, Fe and Mn) in the green and senesced needles and their corresponding resorption efficiency and resorption proficiency. Our results showed that N addition had positive effects on concentrations of N, Al and Mn, negative effects on the P concentration and the Ca concentration in 2014, and neutral effects on concentrations of C, K, Mg and Fe in green needles. N addition signifi-cantly increased foliar N/P. These stoichiometric responses were N level-dependent (stronger at high N rate). N addition significantly decreased N resorption efficiency in 2015 and increased that of K in 2014. Compared with the resorption efficiency, resorption proficiency responded more strongly to increased available N. N addition significantly decreased resorption proficiency of N, and increased that of P, K, and the concentration of Fe in senesced needles, however, there were no significant effects on the concentrations of Ca, Mg, Al and Mn in senesced needles. We concluded that responses of foliar stoichiometry to N addition were element-specific, and plants might cope with changing environments via adjusting internal nutrient cycle (resorption). The elevated foliar N/P and K/P suggested a shift from N and P co-limitation to P limitation with N additions, and increased concentrations of Al and Mn might imply potential toxicity of metal ions to P. elliottii.

[Effects of nitrogen additions on soil hydrolase and oxidase activities in Pinus elliottii plantations.] / æ°®æ·»åŠ å¯¹æ¹¿åœ°æ¾æž—åœŸå£¤æ°´è§£é ¶å’Œæ°§åŒ–é ¶æ´»æ€§çš„å½±å“.

We evaluated responses of hydrolase and oxidase activities in a subtropical Pinus elliottii plantation through a nitrogen (N) addition field experiment (dosage level: 0, 40, 120 kg N·hm-2·a-1). The results showed that N additions significantly decreased the carbon, nitrogen and phosphorus related hydrolase and oxidase activities. The activities of ß-1,4-glucosidase (BG), cellobiohydrolase (CBH), ß-1,4-N-acetylglucosaminidase (NAG) and peroxidase (PER) activities were decreased by 16.5%-51.1% due to N additions, and the decrease was more remarkable in the higher N addition treatment. The activities of α-1,4-glucosidase (aG), ß-1,4-xylosidase (BX), acid phosphatase (AP) and phenol oxidase (PPO) were decreased by 14.5%-38.6% by N additions, however, there was no significant difference among the different N addition treatments. Soil enzyme activities varied obviously in different seasons. The activities of BG, NAG, BX, CBH, AP and PPO were in the order of March > June > October, and aG and PER activities were in the order of October > March > June. Most of the soil hydrolase and oxidase activities were positively correlated with soil pH, but negatively with NO3--N content. It indicated that N additions inhibited soil hydrolase and oxidase activities by reducing soil pH and increasing soil nitrification. N additions inhibited the soil organic matter mineralization and turnover in the subtropical area, and the effects were obvious with the increasing dosage of N additions.

Effect of oral esomeprazole on recurrent bleeding after endoscopic treatment of bleeding peptic ulcers.

BACKGROUND: After endoscopic treatment of bleeding peptic ulcer, a high-dose infusion of omeprazole substantially reduces the risk of recurrent bleeding. The role of oral proton pump inhibitors for these patients is uncertain. The purpose of the present study was to assess whether the use of oral esomeprazole would reduce the frequency of recurrent bleeding after endoscopic treatment of bleeding peptic ulcers. METHODS: Patients with actively bleeding ulcers or ulcers with non-bleeding visible vessels were treated with an epinephrine injection followed by thermocoagulation. After hemostasis had been achieved, they were randomly assigned in a double-blind fashion to receive esomeprazole (40 mg p.o. twice daily for 3 days) or placebo. The outcome measures studied were recurrent bleeding, blood transfusion requirement, surgery and death. RESULTS: A total of 70 patients were enrolled, 35 in each group. Bleeding recurred within 30 days in two patients (5.7%) in the esomeprazole group, as compared with three (8.6%) in the placebo group (P = 0.999). Blood transfusion requirement was 2.8 +/- 1.4 units in the esomeprazole group and 2.7 +/- 1.3 units in the placebo group (P = 0.761). Duration of hospitalization was 4.82 +/- 1.8 days in the esomeprazole group and 4.58 +/- 2.7 days in the placebo group (P = 0.792). No patients needed surgery for control of bleeding and no patients died in both groups. CONCLUSIONS: After successful endoscopic treatment of bleeding peptic ulcer, oral use of esomeprazole might offer no additional benefit on the risk of recurrent bleeding.