Benefits of biochar, compost and biochar–compost for soil quality, maize yield and greenhouse gas emissions in a tropical agricultural soil

The centenary of Hiltner's recognition of a rhizosphere effect is a convenient point to assess the impact of such thinking on the direction of soil science. A review of the major soil journals suggests that for much of the last century, Hiltner's insight had little effect on mainstream thinking outside of soil microbiology, but this situation is changing rapidly as the consequences of spatial and temporal heterogeneity on soil functioning assumes greater importance. Studies of root growth, root distributions and of rhizosphere processes over the last 25 years demonstrate both the size and distribution of root systems and the associated inputs from roots to soils. These inputs result in a plethora of dynamic reactions at the root-soil interface whose consequences are felt at a range of temporal and spatial scales. Root growth and respiration, rhizodeposition, and uptake of water and nutrients result in biological, chemical and physical changes in soils over variable distances from the root surface so that the rhizosphere has different dimensions depending on the process considered. At the root length densities common for many crop species, much of the upper 0.1 m of soil might be influenced by root activity for mobile nutrients, water and root-emitted volatile compounds for a substantial proportion of the growing season. This brief review concludes that roots are an essential component of soil biology and of soil science.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2389.2005.00778.x

Roots, rhizosphere and soil: the route to a better understanding of soil science?

Spatial point pattern analysis provides a statistical method to compare an observed spatial pattern against a hypothesized spatial process model. The G statistic, which considers the distribution of nearest neighbor distances, and the K statistic, which evaluates the distribution of all neighbor distances, are commonly used in such analyses. One method of employing these statistics involves building a simulation envelope from the result of many simulated patterns of the hypothesized model. Specifically, a simulation envelope is created by calculating, at every distance, the minimum and maximum results computed across the simulated patterns. A statistical test is performed by evaluating where the results from an observed pattern fall with respect to the simulation envelope. However, this method, which differs from P. Diggle's suggested approach, is invalid for inference because it violates the assumptions of Monte Carlo methods and results in incorrect type I error rate performance. Similarly, using the simulation envelope to estimate the range of distances over which an observed pattern deviates from the hypothesized model is also suspect. The technical details of why the simulation envelope provides incorrect type I error rate performance are described. A valid test is then proposed, and details about how the number of simulated patterns impacts the statistical significance are explained. Finally, an example of using the proposed test within an exploratory data analysis framework is provided.

Statistical inference using the g or K point pattern spatial statistics.

The responses of Quercus robur (oak) and Fagus sylvatica (beech) seedlings to four different light environments (full, 50%, 40% and 15% sunlight) and to a rapid increase in irradiance were explored during the summer, after 2 years of growth in a forest nursery at Nancy (France). Significant differences between the two species were found for most variables. Phenotypic plasticity for morphological variables (root-shoot ratio, leaf size, leaf weight ratio) was higher in beech than in oak, while the reverse was true for anatomical (stomatal density, epidermis thickness, exchange surface area of the palisade parenchyma) and physiological (maximum photosynthetic rate, stomatal conductance, Rubisco activity) variables. Predawn photochemical efficiency (F
 v/F
 m) was higher in oak than in beech in all light environments except in 15% sunlight. F
 v/F
 m was significantly lower in 100% sunlight than in the other light environments in beech but not in oak. Maximum photosynthetic rates (A
 max) increased with increasing light availability in the two species but they were always higher in oak than in beech. Oak exhibited higher Rubisco activity than beech in full sunlight. The transfer of shade-adapted seedlings to the open caused a decrease of F
 v/F
 m, which was larger for beech than for oak. Transferred oak but not beech plants recovered gradually to the control F
 v/F
 m values. The decreased chlorophyll content and the increased non-photochemical quenching observed in high-light beech seedlings were not enough to avoid photoinhibition. The results suggest that a greater tolerance of strong irradiance is linked to an enhanced physiological plasticity (variables related to photosynthesis), while shade tolerance relies on an enhanced plasticity in light-harvesting variables (crown morphology and chlorophyll content).

The greater seedling high-light tolerance of Quercus robur over Fagus sylvatica is linked to a greater physiological plasticity

Biochar and biochar-compost as soil amendments: effects on peanut yield, soil properties and greenhouse gas emissions in tropical North Queensland, Australia

Effects of light and soil fertility on growth, leaf chlorophyll content and nutrient use efficiency of beech (Fagus sylvatica L.) seedlings

Effects of changing light conditions on the ecophysiological condition behind survival were examined on beech from two different populations. Plants were grown in a greenhouse under simulated understorey and canopy gap light conditions. Upon exposure to high light maximum photosynthesis of shade-acclimated leaves increased followed by a reduction over several days to between high- and low-light control rates. In the reciprocal transfer, the decrease in maximum photosynthesis was rapid during the first 2–3 days and then levelled off to values comparable to low-light controls. Seedlings from Sicily (Madonie) showed generally higher maximum photosynthetic rates than those from Abetone. Leaf conductance varied in the same direction as photosynthesis in high- to low-light seedlings but to a lesser degree. Leaves grown under low light and exposed to high light experienced photoinhibition. The Abetone population was more susceptible to photoinhibitory damage than the seedlings from Sicily. Exposure to high light of shade-acclimated seedlings resulted in intermediate chlorophyll concentrations between levels of the high-light and low-light seedlings. Carotenoid concentration was unaffected by treatments. Seedlings grew more in high light, but had a lower leaf area ratio. Light-limited seedlings showed a shift in carbon allocation to foliage. Leaves formed in the new light regime maintained the same anatomy that had been developed before transfer. Seedlings from Sicily had thicker leaves than those of seedlings from Abetone. Seedlings from Abetone were found to be more susceptible to changing light conditions than seedlings from Sicily. We conclude that small forest gaps may represent a favorable environment for photosynthesis and growth of beech regeneration as a result of the limited ability of seedlings to acclimate to sudden increases in high irradiance and because of the moderate levels of light stress in small gaps.

Acclimation to changing light conditions of long-term shade-grown beech (Fagus sylvatica L.) seedlings of different geographic origins

In a 0.75-ha plot in a Norway spruce (Picea abies Karst.)  silver fir (Abies alba Miller) stand in Comelico (Italian eastern Alps), we analysed (i) the distribution and growth of natural regeneration of Norway spruce and silver fir as affected by stand structure and (ii) the age structure of all saplings between 0.2 and 10 m in height in a 30-year-old gap. In both species, most natural regeneration was clumped and located at the margin of the gaps; however, fir saplings were more represented in understorey environments and less represented in gaps as compared with spruce. Age structure of natural regeneration in the selected gap revealed that the majority (75%) of saplings appeared after the formation of the gap; however, for regeneration taller than 2 m (which has a better chance of reaching the uppermost canopy layer), saplings already present at gap formation predominated. We conclude that (i) gap edges represent a preferential regeneration niche in this forest and (ii) saplings established before gap...

Dynamics of Norway spruce and silver fir natural regeneration in a mixed stand under uneven-aged management

The survival and growth of natural beech regeneration after canopy removal is variable and little is known about ecophysiological mechanisms of these responses. Biomass, nonstructural carbohydrate levels and nitrogen concentrations were measured in an Italian population of European beech seedlings. Seedlings were container-grown in two types of soil, organic and mineral, collected at the study site. The seedlings were grown under three light treatments: under full beech canopy (understory), exposed to full sun only during midday (gap) and under full sun (clearing). Leaf gas exchange and chlorophyll α fluorescence parameters were measured and then foliar analyses were conducted for chlorophyll, phenolic and tannin levels. Biomass and allocation were significantly affected by light and soil treatments. The clearing seedlings and those in organic soil were larger than seedlings in the other light treatments or soil type. Total nonstructural carbohydrate concentrations were lower in the understory seedlings and significant differences between soil types were present in the gap and clearing seedlings. Nitrogen concentrations were higher in the understory seedlings and those growing in the organic soil compared to the other treatments. Gas exchange rates were highest in clearing and the organic soil seedlings. Gap seedlings exhibited photosynthetic acclimation that allowed them to utilize high light of midday and any sunflecks during the morning and afternoon. Relative fluorescence was significantly influenced by both light treatment and soil type, with the highest values observed in the gap seedlings. Light response curves showed decreasing apparent maximum quantum efficiency from the understory to clearing, while maximum photosynthetic rate was highest in the gap seedlings. Chlorophyll concentration was highest in understory seedlings and those growing in organic soil and higher in seedlings growing in organic than in mineral soil. Both foliar tannin and phenolic levels were highest in clearing seedlings, and only tannin concentrations were affected by soil type. Understory seedlings had the highest mortality and insect herbivory; the latter was found to be inversely related to tannin concentration. ()verall, growth and photosynthesis in beech seedlings responded positively to high light associated with small canopy gaps. Organic soil increased seedling size, particularly in the gap and clearing environments. We conclude that forest gaps are favorable for photosynthesis and growth of European beech seedlings.

Ecophysiological responses of Fagus sylvatica seedlings to changing light conditions. II. The interaction of light environment and soil fertility on seedling physiology

Gianfranco Minotta

Papers

Effects of light and soil fertility on growth, leaf chlorophyll content and nutrient use efficiency of beech (Fagus sylvatica L.) seedlings

Acclimation to changing light conditions of long-term shade-grown beech (Fagus sylvatica L.) seedlings of different geographic origins

Dynamics of Norway spruce and silver fir natural regeneration in a mixed stand under uneven-aged management

Ecophysiological responses of Fagus sylvatica seedlings to changing light conditions. II. The interaction of light environment and soil fertility on seedling physiology

Environment-induced Modifications to Root Longevity in Lolium perenne and Trifolium repens