Soil Acidification in Nutrient-Enriched Soils Reduces the Growth, Nutrient Concentrations, and Nitrogen-Use Efficiencies of Vachellia sieberiana (DC.) Kyal. & Boatwr Saplings.

Nitrogen (N) and phosphorus (P) nutrient enrichment is important for grasslands. This study aimed to determine how soils enriched with N and P influenced soil concentration correlations and affected the growth kinetics, mineral nutrition, and nitrogen-use efficiencies of Vachellia sieberiana grown in a greenhouse experiment. The soils used as the growth substrate were analysed and showed extreme acidity (low soil pH, 3.9). Nitrogen-enriched soils were more acidic than P-enriched soils. Exchangeable acidity was strongly negatively correlated with an increase in soil pH, with soil pH between 3.9 and 4.1 units showing the strongest decline. Plant saplings showed increased root biomass, shoot biomass, total biomass, and plant N and P concentrations when grown in soils with high soil P concentrations. Extreme soil acidification in N-enriched soil was one of the main factors causing P unavailability, decreasing sapling growth. Extreme soil acidification increased concentrations of toxic heavy metals, such as Al which may be alleviated by adding lime to the extremely acidic soils. Research implications suggest that soil pH is an important chemical property of the soil and plays a significant role in legume plant growth. Legume species that are unable to tolerate acidic soils may acquire different strategies for growth and functioning.

Offspring diet supersedes the transgenerational effects of parental diet in a specialist herbivore Neolema abbreviata under manipulated foliar nitrogen variability.

Diet quality influences organismal fitness within and across generations. For herbivorous insects, the transgenerational effects of diet remain relatively underexplored. Using a 3 × 3 × 2 factorial experiment, we evaluated how N enrichment in parental diets of Neolema abbreviata (Larcordaire) (Coleoptera: Chrysomelidae), a biological control agent for Tradescantia fluminensis Vell. (Commelinaceae), may influence life history and performance of F1 and F2 offspring under reciprocal experiments. We found limited transgenerational effects of foliar nitrogen variability among life-history traits in both larvae and adults. Larval weight gain and mortality were responsive to parental diet contrary to feeding damage, pupal weight and duration taken to pupate. There were significant parental diet × test interactions in larval feeding damage, weight gain, pupal weight and time to pupation. Generally, offspring from parents under high N plants performed better even under low N test plants. Adult traits including oviposition selection, feeding weight and longevity did not respond to the effects of parental diet nor its interaction with test diet as was the case in the larval stage. However, the main effects of test diet were more important in determining adult performance in both generations suggesting limited sensitivity to parental diet in the adult stage. Our results show conflicting responses to parental diet between larvae and adults of the same generation among an insect species with both actively feeding larval and adult life stages. These transgenerational effects, or lack thereof, may have implications on the field performance of N. abbrevita under heterogeneous nutritional landscapes.

The effects of abiotic factors in South African semi-arid grassland communities on Seriphium plumosum L density and canopy size.

Most studies suggest that multiple factors are responsible for woody plant encroachment, but are inconclusive on its causes. Woody plant encroachment is modified by local patterns of disturbance, topography, soil texture and fertility, and their relative importance and interaction strength varies among locations. We used grassland communities, Carletonville Dolomite Grassland (CDG), Rand Highveld Grassland (RHG) and abiotic factors (Soil Organic Carbon (SOC), Total nitrogen (TN), Phosphorus (P), Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg) and pH) to investigate habitat preferences of Seriphium plumosum L. in South African semi-arid grassland. Grassland community had a significant effect on S. plumosum density, canopy size, and on components of soil fertility (P< 0.05). Slope position had a significant effect on S. plumosum density and canopy size (P< 0.05). Seriphium plumosum density was significantly lower (23 plants/50 m2±2.39 (SE)) in CDG than in RHG (40 plants/50 m2±4.19). By contrast, S. plumosum canopy size was significantly higher (1.39 m2±0.11) at CDG than at the RHG (1.06 m2±0.08). The interaction of grassland community and slope position had a significant effect on S. plumosum density and soil sodium content (P< 0.05). Bottom slope regions in RHG (59.00 plants/50 m2±8.62) had higher S. plumosum density than bottom slope regions (19.75 plants/50 m2±3.01) in CDG. Soil sodium content was similar in CDG slopes and higher than in RHG slopes. Seriphium plumosum density was positively related to components of soil fertility; P (r2 = 0.1270; P 0.0036), K (r2 = 0.0786; P 0.0237), Na (r2 = 0.0686; P 0.0350), Ca (r2 = 0.0681; P 0.0358), and SOC content (r2 = 0.0669; P 0.0374). However, Seriphium plumosum canopy size did not show any relationship with components of soil fertility. This study revealed that S. plumosum density in grassland communities increased with increasing soil texture and fertility.