[Soil carbon, nitrogen and phosphorus stoichiometry characteristics of Pinus sylvestris var. mongolica belt-mixed forests.] / 沙地樟子松带状混交林土壤碳氮磷化学计量特征.

To provide theoretical basis for management of Pinus sylvestris var. mongolica mixed plantation, the variation of soil carbon, nitrogen and phosphorus stoichiometry in different P. sylvestris var. mongolica belt-mixed plantations were explored. Taking the monoculture plantation as control, soil samples were collected at the distance of 0, 1, 2, 3, and 4 m from the center point in P. sylvestris var. mongolica and Ulmus pumila mixed plantation and P. sylvestris var. mongolica and Maackia amurensis mixed plantation along the two directions of P. sylvestris var. mongolica and its associated species in different soil layers. Contents and stoichiometric ratios of soil organic C, total N, total P, available N, available P were analyzed. The results showed that soil organic C, total N, and available N in P. sylvestris var. mongolica mixed plantations were higher than those in pure plantation. The soil organic C, total N contents, C/N and C/P in deep soil layers were increased under P. sylvestris var. mongolica and U. pumila mixed plantation. The soil N content increased but P content decreased in P. sylvestris var. mongolica and M. amurensis mixed plantation. With the increases of distance from the center of mixed plantation, soil C/N firstly increased and then decreased, while soil total P and available P contents decreased and N/P increased in P. sylvestris var. mongolica belt. Soil C/N decreased and available P contents firstly increased and then decreased with the increases of distance from the center in U. pumila belt of P. sylvestris var. mongolica and U. pumila mixed plantation. Soil total N content firstly decreased and then increased in P. sylvestris var. mongolica belt, but it firstly increased and then decreased in M. amurensis belt of P. sylvestris var. mongolica and M. amurensis mixed plantation. P. sylvestris var. mongolica mixed plantation could improve soil C and N stocks compared with pure plantation. The best mixed mode was P. sylvestris var. mongolica and U. pumila mixed by one row, as well as P. sylvestris var. mongolica and M. amurensis mixed in two rows.

[Changes of non-structural carbohydrates of Pinus sylvestris var. mongolica seedlings in the process of drought-induced mortality]. / 沙地樟子松幼苗干旱致死过程中非结构性碳水化合物的变化.

To understand the distribution of non-structural carbohydrates (NSC) and adaptive mechanism in the process of drought-induced mortality, two-year-old Pinus sylvestris var. mongolica seedlings were grown under continuous natural drought condition. Needle water potential and the contents of soluble sugar, starch and total NSC in different organs (current-year-old needles, one-year-old needles, stems, coarse roots and fine roots) of the seedlings were measured when soil water content decreased to 60%, 40%, 30%, 20% and 15% of the soil field water capacity (SFC). The results showed that when the soil water content decreased from 40% SFC to 15% SFC, there was no significant change in needle water potential at predawn and midday. When soil water content decreased from 60% SFC to 30% SFC, the contents of soluble sugar, starch, total NSC and the ratio of soluble sugar and starch first decreased and then increased in all organs. When soil water content dropped from 30% SFC to 20% SFC, the soluble sugar, starch and total NSC contents decreased in the current-year-old needles, one-year-old needles, stems and fine roots. The soluble sugar content increased, but the starch and total NSC contents decreased in the coarse roots. When soil water content decreased from 20% SFC to 15% SFC, the contents of soluble sugar, starch and total NSC decreased in the current-year-old needles, one-year-old needles and stems, and the soluble sugar and total NSC contents decreased, but the starch content increased in the coarse roots, the soluble sugar content decreased, but the starch and total NSC contents increased in fine roots. The results indicated that NSC content in different organs of P. sylvestris var. mongolica seedlings varied in their adaptation to different degrees of drought. The contents of soluble sugar and total NSC in seedlings decreased under less than 30% of the soil field water capacity, with the starch being accumulated in the coarse roots and fine roots. The seedlings might be died due to carbon depletion.

[Needles stable carbon isotope composition and traits of Pinus sylvestris var. mongolica in sparse wood grassland in south edge of Keerqin Sandy Land under the conditions of different precipitation].

A comparative study was conducted on the needles stable carbon isotope composition (delta13 C), specific leaf area (SLA), and dry matter content (DMC) of 19-year-old Pinus sylvestris var. mongolica trees in a sparse wood grassland in the south edge of Keerqin Sandy Land under the conditions of extreme drought and extreme wetness, aimed to understand the water use of Pinus sylvestris under the conditions of extreme precipitation. The soil water content and groundwater level were also measured. In the dry year (2009), the soil water content in the grassland was significantly lower than that in the wet year (2010), but the delta13C values of the current year-old needles had no significant difference between the two years and between the same months of the two years. The SLA of the current year-old needles was significantly lower in the dry year than in the wet year, but the DMC had no significant difference between the two years. Under the conditions of the two extreme precipitations, the water use efficiency of the trees did not vary remarkably, and the trees could change their needles SLA to adapt the variations of precipitation. For the test ecosystem with a groundwater level more than 3.0 m, extreme drought could have no serious impact on the growth and survival of the trees.