Phosphorus fractions and phosphomonoesterase activities in sandy soils under a temperate savanna and a neighboring Mongolian pine plantation

To assess the effects of savanna afforestation on soil phosphorus （P） transformations in eastern Horqin Sandy Land, China, P fractions and phosphomonoesterase activities were examined in two soil horizons （0-5 cm and 5-20 cm） under a savanna and an adjacent 30-year-old Mongolian pine （Pinus sylvestris L. vat. mongolica Litv.） plantation on a P-deficient semi arid sandy soil. The results showed that all soil P fractions and phosphomonoestcrase activities decreased with soil depth at both sites except that labile organic P under the plantation was constant with soil depth, In contrast to savanna, soils trader Mongolian pine plantation had lower phosphomonoesterase activities and concentrations of all P fractions （with an exception of Al-P）, lower proportions of organic P and Ca-P in total P, and higher proportions of labile P, Al-P and Fe-P in total P. These results suggested that P transformations mainly occurred in surface soils, and P recycled through litterfall was the most important source of plant available P. Mongolian pine afforestation enhanced the bioavailability of both organic P and Ca-P. simultaneously reduced soil P pools. indicating that protection of forest floor and P fertilization are necessary to maintain the sustainable functioning of Mongolian pine plantations.

Impacts of short-term nitrogen addition on the thallus nitrogen and phosphorus balance of the dominant epiphytic lichens in the Shennongjia mountains, China

Aims To better understand whether and how nitrogen addition impacts the epiphytic lichens in the Shennongjia Nature Reserve(China).Methods Five dominant epiphytic lichen species,including Usnea longis-sima,U.luridorufa,Ramalina calicaris var.japonica,U.dasopoga and U.betulina,were selected as materials,and then field and la-boratory nitrogen addition experiments were performed.The phos-phomonoesterase(PME)activity and nitrogen(N)and phosphorus(P)content of these lichens were measured,and then the effects of nitrogen addition on thallus nutrient balance and PME activity were discussed.Important Findings Our results showed that with an increased N deposition from 0.6 to 50 kg N ha^(−1) a^(−1),the thallus N content of the five lichen species increased significantly,suggesting that those lichens had strong ability to take up and accumulate N,and an universality of N intolerance in epiphytic lichens.Meanwhile,the P content of five lichens increased slower than N content among N treatments,indicating the supply of P was deteriorated when the supply of N increased.The N addition also led to the N:P ratios of five lichens increased from about 10 to 20,and reached a maximum at 50 kg N ha^(−1) a^(−1),and the PME activity of the five lichen species was upregulated by the N addition,indicated that the balance between N and P was deteriorated in these lichens.We concluded that in-creases in N deposition will lead to nutrient imbalance in lichens and that nitrogen enrichment will change these five lichen species from being N limited to being P limited.Our research will be of value in the conservation of lichen diversity in the Shennongjia Nature Reserve(China).