Nian-Xi Zhao

RAPD diversity of Stipa grandis populations and its relationship with some ecological factors

The genetic diversity of Stipa grandis P.Smirn and its relationship with the climatic variables were studied using the RAPD technique for 90 genes from five natural populations sampled in the Xilingol steppe, China. Sixteen oligonucleotides screened from 100 random primers were used to amplify 310 trackable RAPD loci, which were all polymorphic. By analyzing the RAPD data using POPGENE software, different geographic S. grandis populations were studied, which indicated a high level of genetic diversity, and the maximum variation was observed within the populations with a 28% variation observed among the populations. Using Pearson correlation analysis, significant (P < 0.05) or highly significant (P < 0.01) relationships were found between gene diversity indexes and temperature factors (≥10°C cumulative temperature in a year, annual mean temperature and mean temperature in January). Mantels tests showed that there was no significant correlation between Neis unbiased genetic distance and the geographic distance of S. grandis populations (r = 0.184, P = 0.261). However, there were significant or highly significant correlations between Neis genetic distance and the several climatic divergences in pairwise S. grandis populations. All results indicated that natural selection resulting from variations in water and temperature was responsible for the adaptive eco-geographical differentiation indicated by the RAPD markers of different S. grandis populations, and that immigration and gene drift did not play an important role in affecting the differentiation of S. grandis populations.

RAPD analysis of genetic diversity and population genetic structure of Stipa krylovii reshov. in Inner Mongolia steppe

Random amplified polymorphic DNA (RAPD) analysis was used to characterize the genetic diversity and population genetic structure of Stipa krylovii populations in Inner Mongolia steppe of North China. Thirteen 10-bp oligonucleotide primers, which generated 237 RAPD bands, were used to analyze 90 plants of five populations from three regions, meadow steppe, typical steppe and desert steppe, from the east to the west. The genetic diversity of Stipa krylovii that was revealed by observed number of alleles (na), expected number of alleles (ne), Nei’s diversity index (h), Shannon’s diversity index (H), amplificated loci, polymorphic loci and the percentage of polymorphic loci (PPB) increased from the east to the west. The Pearson’s correlation analysis between genetic diversity parameters and ecological parameters indicated that the genetic diversity of Stipa krylovii was associated with precipitation and cumulative temperature variations along the longitude (humidity were calculated by precipitation and cumulative temperature). Dendrogram based on Jaccard’s genetic distance showed that the individuals from the same population formed a single subgroup. Although most variation (56.85%) was within populations, there was high genetic differentiation among populations of Stipa krylovii, high differentiation within and between regions by AMOVA analysis. Either Nei’s unbiased genetic distance (GST) or gene flow (Nm) among pairwise populations was not correlated with geographical distance by Mantel’s test (P > 0.05), suggesting that there was no consistency with the isolation by distance model in these populations. Natural selection may have played a role in affecting the genetic diversity and population structure, but habitat destruction and degradation in northem grassland in China may be the main factor responsible for high genetic differentiation among populations, within and among regions.

Genetic diversity and population differentiation of the dominant species Stipa krylovii in the Inner Mongolia Steppe.

Random amplified polymorphic DNA was used to assess the level of genetic diversity and genetic structure of Stipa krylovii (Gramineae), an important dominant species in the northern grasslands of China. Genetic diversity was low within S. krylovii populations, and diversity at the population level was associated with precipitation and cumulative temperature variations. There was much genetic differentiation among populations and among habitats as well. A Mantel test indicated no significant correlation between genetic distance and geographic distance of populations. A nonmetric multidimensional scaling analysis revealed some spatial relationships among the 90 individuals in a two-dimensional plot. Habitat fragmentation and degradation throughout the geographic range of S. krylovii could account for the low genetic diversity and high genetic differentiation of the species. Such information will be useful for conservation managers trying to plan an effective strategy to protect this important species.

Influence of Nitrogen Fertilizer and Endophyte Infection on Ecophysiological Parameters and Mineral Element Content of Perennial Ryegrass

An experiment was designed to determine the effect of the fungal endophyte Neotyphodium lolii on the growth, physiological parameters and mineral element content of perennial ryegrass (Lolium perennel L.), when growing at two N supply levels. Endophyte infection had a significant positive effect on both shoot and root growth of ryegrass, but this difference was only significant in the high N supply treatment. At high N supply, endophyte-infected (EI) plants accumulated more soluble sugar in the sheath and the root than endophyte-free (EF) plants. Endophyte infection affected mineral element concentrations in the root more than in the shoot. We found a significant effect of endophyte infection on B, Mn and Mg in the root, but significant effect was only found on B in the shoot. EI plants tended to accumulate less B in the shoot at both N levels, but accumulated more B, Mn and Mg in the root at low N levels. The difference of growth parameters in different periods was significant. The content of soluble sugar and crude protein in the sheath were also dependent on the growth stages of both EI and EF plants.

Genetic variation among Stipa grandis P. Smirn populations with different durations of fencing in the Inner Mongolian Steppe

The genetic structure of a population should be carefully considered in ecological restoration because it may play a critical role in maintaining the persistence of a restored ecosystem. In the present study, we examined genetic diversity and genetic structure of Stipa grandis P. Smirn populations from fenced and grazed plots using amplified fragment length polymorphism markers. Molecular genetic variation showed that the genetic diversity of the fenced populations was greater compared with the overgrazed population. There was a significant variation among the populations (Fst = 0.3689, P < 0.001) by AMOVA analysis, and the gene flow was 0.4039 among the populations. The results from a comparison of limited morphological characteristics and from an unweighted pair group method with arithmetic mean cluster analysis and non-metric multi-dimensional scaling analysis suggested that genetic differentiation had occurred between the fenced populations and the grazed populations. The largest genetic diversity was in the moderately grazed population, which might be related to higher population density and greater sexual reproduction due to less disturbances in the plots. The genetic diversity of the long-term (24 years) fenced population was similar to that of a short-term fenced population (fenced for 11 years). These results suggested that the genetic diversity in the overgrazed population might be increased to some extent through fencing, but this effect did not occur beyond 11 years.

Ecophysiological response in leaves of Caragana microphylla to different soil phosphorus levels

Phosphorus (P) is one of the limiting mineral nutrient elements in the typical steppe of Inner Mongolia, China. In order to find out the adaptive strategy of Caragana microphylla to low soil P status, we grew plants in P-deficient soil in April 2009 and gave a gradient of P addition ranging from 0 to 60 mg(P) kg−1(soil) from May 2010. Leaf traits were measured in September 2010. Both leaf growth and light-saturated photosynthetic rate (Pmax) were similar among different groups. Leaf nitrogen (N):P ratio indicated that the growth of C. microphylla was not P-limited in most of the Inner Mongolia typical steppe, which had an average soil available P content equal to 3.61 mg kg−1. The optimal P addition was 20 mg(P) kg−1(soil) for two-year-old plants of C. microphylla. Leaf mass area (LMA) and leaf dry matter content (LDMC) were enhanced with low P, and significantly negatively correlated with photosynthetic N-use efficiency (PNUE). Photosynthetic P-use efficiency (PPUE) increased with decreasing soil P and increasing leaf inorganic P (Pi): organic P (Po) ratio, and showed no significant negative correlation with LMA or LDMC. Pmax of C. microphylla did not decline so sharply as it was anticipated. The reason for this phenomenon might be due to the increased PPUE through regulating the leaf total P allocation. C. microphylla had high P-use efficiency via both high PPUE and long P-retention time at low-P supply. The adaptation of C. microphylla to low-P supply provided a new explanation for the increased distribution of the species in the degraded natural grassland in Inner Mongolia, China.