Fixed allocation patterns, rather than plasticity, benefit recruitment and recovery from drought in seedlings of a desert shrub

Differences in Allometric Relationship of Two Dominant Woody Species Among Various Terrains in a Desert Region of Central Asia

The allometric relationship among different functional traits is an ecological strategy for plants to promote resource utilization, which indicates the ability of plants to adapt to environmental changes coordinately. In this study, we conducted a field survey on Haloxylon ammodendron and H. persicum among different terrains (dune crest, eastern slope, western slope and inter-dune) in the Gurbantunggut Desert, obtained their quantitative and morphological characteristics, and analyzed their allometric relationships between plant height and canopy radius, plant height and basal diameter by using standardized major axis estimation. We found that: (1) The dominated terrains of H. ammodendron and H. persicum were different; (2) The individual morphology of the two Haloxylon species changed significantly with the terrains (p < 0.05), with the largest and smallest ones growing on the eastern slope and the inter-dune lowland, respectively; (3) Fixed allometric patterns were observed in the above-ground parts of the two Haloxylon species, as the growth of canopy and basal stem was preferentially to plant height; (4) These allometric relationships were significantly affected by the terrain, and exhibited discrepancy between two species, they both invested less in plant height in windy habitats, such as the dune crest and western slope, but H. ammodendron growing on the western slope and H. persicum growing on the eastern slope invested more in basal diameter for strengthening mechanical support and resources acquisition, respectively. These results indicated that both studied species adopted an ecological strategy that allocating more resources to horizontal expansion rather than vertical growth, the terrain has an important influence on the allometric relationship of their above-ground parts, and the trade-off mechanism of main components investing was different for these two species due to habitat heterogeneity and ecological adaptability.

Spatial Distribution and Structural Characteristics for Haloxylon ammodendron Plantation on the Southwestern Edge of the Gurbantünggüt Desert

Haloxylon ammodendron (C.A.Mey.) Bge. is crucially important for stabilizing sand dunes in the desert area of the Junggar Basin and has thus been widely planted in the oasis–desert ecotone for windbreak and sand fixation purposes since the 1980s. The spatial distribution and structural characteristics of Haloxylon ammodendron plantations of three different ages—planted in 1983 (36a), 1997 (22a), and 2004 (15a)—on the southwestern edge of the Gurbantünggüt Desert were studied. The results showed that the spatial distribution patterns for the different stages of growth showed a trend of cluster that was random during the transformation from seedlings to juvenile and mature trees. Forest density for the 15a, 22a, and 36a plantations was, respectively, 1110, 1189, and 1933 plants ha−1; the base stem diameter for the main forest layer was 5.85, 8.77, and 6.17 cm, respectively, and the tree height was concentrated in the range of 1.5–3.0 m, 2.0–3.5 m, and 1.5–2.5 m. In the regeneration layers, the proportion of seedlings was the largest in all three stand ages, followed by juvenile trees, and mature trees only appeared in the 22a plantation. The proportion of deadwood in the 36a forest was the highest, and there were no mature trees in the regeneration layer. These results indicate that the three Haloxylon ammodendron plantation stages were in the period of rising at 15a, stable and degenerate with increasing age at 22a, and at 36a the regeneration ability was very weak and presented degradation due to species competition for soil moisture, because of too many seedlings and mature plants. In this case, measures such as thinning could be taken to prevent rapid degradation and to accelerate regeneration when the stand age exceeds 20 years. Considering the sand fixation effect, the pressure of competition for water resources, and forest capacity for renewal and sustainability, the most suitable forest density in the Haloxylon ammodendron plantation would be 8.5–9 m2 per plant.

Growth and carbohydrate dynamic of perennial ryegrass seedlings during PEG-simulated drought and subsequent recovery

Due to the increasing occurrence of drought events, drought recovery has become equally important as drought resistance for long-term growth and survival of plants. However, information regarding the mechanism that controls growth recovery of herbaceous perennials is not available. In this study, perennial ryegrass (Lolium perenne) was rewatered after eight-day exposure to three drought intensities simulated by polyethylene glycol-6000. The growth, nonstructural carbohydrates (NSC, i.e. sucrose, glucose, fructose and starch), shoot δ¹³C, and activities of enzymes for sucrose conversion were monitored for 24 days after rewatering, allowing investigation of the dynamic of NSCs and its relation with growth in the recovery phase. In response to drought, growth and NSC content decreased mainly in shoot rather than root, and the total dry matter was negatively correlated to shoot δ¹³C. After rewatering, the growth of drought-treated groups still lagged behind that of control (CK) group for more than 16 days, but it was no longer correlated to shoot δ¹³C, suggesting that the limited growth is caused by non-stomatal factors related to photosynthesis. On day 24 after rewatering, the final growth of drought-treated groups caught up or even exceeded that of CK group, and was accompanied by higher dry weight root to shoot ratio (R/S) and root NSC content, which may facilitate water and nutrient acquisition and emergency of new tillers, respectively. During drought and subsequent recovery, the variation of R/S and root NSC content mainly attributed to root acid invertase rather than leaf sucrose phosphate synthase activity.