Phosphorus fraction characteristics and influencing factors of soil aggregates in Quercus acutissima pure and mixed forests.

Site conditions more than species identity drive fine root biomass, morphology and spatial distribution in temperate pure and mixed forests

Soil aggregates are important indicators of soil quality and sustainable land utilization, and impact the retention abilities of water and fertilizers and the release of nutrients in soil. This study aimed to understand the effects of two land use types (an orchard and farmland) on the distribution, stability, and organic carbon content of soil aggregates, and provides a theoretical basis for the optimal management of the soil carbon pool in the Weibei Dryland of the Loess Plateau. We examined the soils from an orchard and from farmland by simultaneous sampling and wet sieving; the proportions of large macroaggregates (>2 mm), small macroaggregates (0.25-2 mm), microaggregates (0.053-0.25 mm), and silt and clay (<0.053 mm) were then determined; the content of organic carbon in each aggregate fraction at soil depths of 0-40 cm were also measured, and the total organic carbon content of all aggregates fractions was determined for each soil. The results showed that the type of agricultural land use had a significant effect on the distribution and stability of soil aggregates in the 0-20 cm soil layer, with the relative proportions of the different sized aggregates (>2, 0.25-2, 0.053-0.25, and<0.053 mm) being 12.9%, 51.3%, 28.8%, and 7.0% in the orchards, respectively, and 8.3%, 49.7%, 33.6%, and 8.4% on the farmland, respectively. The proportion of macro-aggregates (>0.25 mm) was significantly higher in the orchard soils than in the farmland soils. Mean weight diameter (MWD) and geometric mean diameter (GMD) are important indicators of the soil aggregate stability; the MWD and GWD of the farmland soils were significantly lower than the orchard soils in the 0-40 cm depth zone (P<0.05). The effects of different land use types on the organic carbon content of soil aggregates was most marked in the 0-10 cm layer. Compared with farmland, the organic carbon content in the large aggregates, intermediate aggregates, micro-aggregates, and the silt and clay fraction of orchard soils were relatively increased by 56.0% (P<0.05), 57.1% (P<0.05), 40.8% (P>0.05), and 13.0% (P>0.05), respectively. Organic carbon storage in each aggregate class (excluding the<0.053 mm fraction) in the orchard soils was higher than in the farmland soils. In the orchard soils, the proportion of soil macro-aggregates (>0.25 mm) and the associated organic carbon content was elevated, damage to aggregates was reduced, and the organic carbon stability was enhanced. In general, the soil aggregate stability and organic carbon content of orchard soils were higher than for the farmland soils. Orchards appear to enhance the physical stability of aggregates with respect to soil organic carbon, contribute to soil organic carbon accumulation, and thus promote soil carbon sequestration.

The aim of this work is the comparative analysis of the productivity of Scots pines in pure and mixed plantations with main and accompanying species in the Northern Steppe of Ukraine We analysed the taxation parameters such as height, diameter, stand density, which vary with the age of the stand and composition of the plantation. Within the study area pines grow mainly in pure stands (81.9%). The share of mixed forest stands in the study area is only 18.1%. The analysis of representation of age structure showed the presence of the same proportion of the young age group in pure and mixed stands, the dominant share being taken up by middle-aged monoculture stands, and thus a smaller area taken up by mature and overmature pines. The average stand density per 1 ha in pure stands of all age groups is 17% higher than in mixed stands. The dynamics of variations of such biometric data as average height, diameter and density for the different compositions of Scots pine stands were measured for 14 age classes. The mean heights of the pure and mixed stands are vere close, while the average diameter gradually increased with age, reaching its maximum in overmature plantations. The research results showed that there is an excess of this parameter in the mixed compared with the pure stands. We did not find significant differences between middle age pure and mixed stands in accumulation of stand density. But pure pine stands show a clear tendency to dominate in wood accumulation in all age classes through the period of growth. The greatest difference between pure and mixed stands in the mean stand density was observed for those of middle-age. The average stand density in the pure stands was up to 32% higher than the mixed. The area distribution of Scots pine stands according to productivity was as follows. The largest area for both pure and mixed stands was occupied by trees of quality class I, which took up 54.3% of the total pure pine acreage and 41.9% of the mixed stand acreage. The second position was occupied by quality class II, which occupied 27.6% of total pure pine acreage and 36.6% of mixed stand acreage with the perecentage of total stand density at 23.6% and 35.1% respectively. In general, the value of the average stand density falls as the quality class decreases, and essentially depends on the composition of plantations: in pure stands, it is higher than in mixed. The investigated values of the biometric parameters are statistically significant for both the pure and the mixed stands.

Root distribution of Norway spruce in monospecific and mixed stands on different soils

This study explored the underground interactions between black spruce and trembling aspen in pure and mixed stands to understand how their soil resource use help these species coexist in the boreal mixedwoods of Western Quebec. We analyzed species-specific fine root foraging strategies (root biomass and root tissue density) along three soil layers (organic, top 0–15 cm, and bottom 15–30 cm mineral soil), using 180 soil cores. We collected cores in three sites, each containing three 20 × 50 m2 plots of pure spruce, pure aspen, and mixed spruce and aspen stands. Spruce had a shallow rooting, whereas aspen had a deep rooting in both types of stands. Compared to pure spruce stands, spruce had a lower fine root biomass (FRB) and a higher root tissue density (RTD) in the organic layer of mixed stands. Both patterns were indicative of spruce’s more intensive resource use strategy and competitive advantage over aspen in that layer. Aspen FRB in the organic soil did not differ significantly between pure and mixed stands, but increased in the mineral soil of mixed stands. Since we did not observe a significant difference in the nutrient content of the mineral soil layer between pure aspen and mixed stands, we concluded that aspen may experience competitive exclusion in the organic layer by spruce. Aspen exhibited an extensive nutrient uptake strategy in the organic layer of mixed stands: higher FRB and lower RTD than spruce. In mixed stands, the differences in aspen rooting patterns between the organic and mineral layers suggested the use of contrasting nutrient uptake strategies along the soil profile. We speculate that the stronger spatial separation of the roots of spruce and aspen in mixed stands likely contribute to a higher partitioning of their nutrient uptake along the soil profile. These results indicate the competitive exclusion of aspen by spruce in boreal mixedwoods, which likely occurs in the soil organic layer.

Forest dynamics are undergoing profound alteration due to the fact that climate change is increasing the frequency and severity of abiotic and biotic forest disturbances. Because of the unpredictable nature of the drought periods and the variation in their severity, Mediterranean forests are typically more vulnerable. Mediterranean Pinus pinaster forests are showing decay symptoms linked to climate change. There is clear evidence that promoting mixtures can serve as an effective forest adaptation strategy. In this regard, we sought to better understand the responses of P. pinaster radial growth dynamics to various factors, in both mixed and pure forest stands, and provide valuable insights into P. pinaster dynamics when mixed with P. sylvestris. In this study, we examined the variation of intra-annual cumulative radial increment patterns in response to the climate of P. pinaster between pure and mixed stands with P. sylvestris. Using data from band dendrometers collected over five consecutive climatically distinct years (2016–2020), a nonlinear mixed-effect model approach was used to analyze the differences in intra-annual cumulative radial increment patterns for P. pinaster between years in mixed and pure stands. The intra-annual radial increment pattern of P. pinaster showed significant year-to-year variation and varied with tree size, with greater increment in larger trees. Trees in mixed stands had a higher mean radial increment compared to corresponding ones in pure stands. Increased summer maximum temperatures negatively affected tree cumulative annual increment regardless of composition, but with a lower impact on trees in pure stands. Spring precipitation increased the length of the growing season, while higher spring maximum temperatures triggered an earlier inflection point. Our results highlight the high plasticity of P. pinaster in adapting to varying intra- and inter-annual environmental conditions and competition with other species and suggest that promoting mixtures with P. sylvestris may be an interesting management strategy for adaptation to climate change.

Soil aggregate stability and organic carbon （SOC） are important indicators of soil structure and quality and play a key role in the improvement of soil quality in temperate deserts. This study aimed to investigate the distribution patterns, stability of soil aggregates, and variation characteristics of the content of aggregate organic carbon in different grassland types in temperate deserts and their interrelationships. Four grassland types in a temperate desert （Kalidium foliatum type, Reaumuria songarica type, Salsola passerina type, and Sympegma regelii type） in the Longzhong Loess Plateau as research objects, and the soil aggregate particle size distribution characteristics were determined using the wet sieving method. The stability of soil aggregates was analyzed by calculating aggregate stability indicators and the contribution of aggregate particle size SOC to bulk soil SOC content. Correlation analysis, principal component analysis, and linear fitting equations were used to reveal the relationship between the soil aggregate content and aggregate particle size SOC and aggregate stability. The results showed that the content of &gt;0.25 mm aggregates （R0.25）, mean weight diameter （MWD）, geometric mean diameter （GMD）, and bulk soil SOC content in each soil layer （0-10, 10-20, and 20-30 cm） of the K. foliatum type grassland were significantly higher than that of the R. songarica type and S. regelii type （P&lt;0.05）. The SOC content of 0.053-0.25 mm and &lt;0.053 mm particle size in each soil layer of the K. foliatum type grassland were significantly higher than that of the S. regelii type （P&lt;0.05）. Surface and subsurface soils （0-10 cm and 10-20 cm） had the significantly highest contribution of 0.25-2 mm particle size SOC to the bulk soil SOC content （P&lt;0.05）. Additionally, as the soil layer deepened, the R0.25, MWD, GMD, bulk soil, and aggregate SOC contents of the K. foliatum type grassland showed a tendency to increase first and then decrease, with the highest contents from 10-20 cm. Kalidium foliatum type grassland aggregate content was dominated by 0.25-2 mm aggregates, whereas the other three grassland types were dominated by 0.053-0.25 mm aggregates. In addition, bulk soil SOC content was significantly correlated with R0.25, MWD, GMD, and ELT （P&lt;0.01）, and the 0.25 mm aggregate was the critical size of positive and negative correlation. R0.25, MWD, GMD, and ELT values were the key factors influencing bulk soil SOC in grassland. The equation fitted to bulk soil SOC content, and GMD was the most suitable to describe the relationship between SOC content and the stability of soil aggregates. Therefore, compared with other grassland types, K. foliatum type grassland had a promoting effect on the soil aggregate stability and the improvement of soil quality.

За матеріалами повидільної бази даних лісовпорядкування проаналізовано формування чистих та мішаних букових деревостанів в умовах свіжої грабової та дубово-грабової бучин. Порівняно з 1996 р. площа рівнинних букових деревостанів збільшилась на 14 тис. га та змінилась структура їх лісового фонду. В умовах свіжого груду найбільші площі букових деревостанів зосередженні у свіжій грабовій (22,5%) та дубово-грабовій (75,7%) бучині. Кількість ділянок мішаних деревостанів більш, ніж у два рази перевищує кількість чистих, але за площею та сумарними запасами чистих і мішаних букових лісостанів відмінність не така суттєва. На запаси чистих деревостанів припадає понад 40% сумарного запасу букових деревостанів.&#x0D; До 25-30 років рівнинні букові деревостани переважно характеризуються І класом бонітету, після 30 років інтенсивність їх росту зростає і на віковому проміжку 30-80 років переважають насадження, де бук характеризується Іа та вищими класами бонітету, але пізніше інтенсивність росту чистих і мішаних деревостанів сповільнюється і вони знову характеризуються І класом бонітету. Середній клас бонітету чистих та мішаних деревостанів – Іа,5. Інтенсивне нагромадження запасів в них спостерігається до 80 років, коли досягає 350 м3/га, але їхні запаси є нижчими, ніж у нормальних деревостанах. Суттєво нижчі запаси досліджуваних деревостанів після 80 років, порівняно з нормальними та модальними деревостанами, свідчать про необхідність кваліфікованого підходу до планування та виконання поступових і вибіркових рубок у букових лісостанах.

In order to restore biodiversity in the degraded forest landscape and to use forest plantations for climate change mitigation, experimental plantations of indigenous trees (including mahogany species) and important exotic trees species like Tectona grandis have been established in pure and in mixed stands in the degraded Tain Tributaries Block II Forest Reserve in the dry semi-deciduous forest zone of Ghana. This study assessed the performance of an important indigenous species, Khaya grandifoliola, in pure and in mixed stands, and compared its performance to the exotic tree species, T. grandis. The results from the study indicated that after 4 years, there was a significant difference in the diameter of K. grandifoliola (P = 0.001) between pure and mixed stands with the pure stands having an average diameter of 9.15 ± 0.19 cm compared with 7.81 ± 0.33 cm for mixed stands. Pure stands had a correspondingly higher basal area at breast height for individual trees in pure stands compared with mixed stands. K. grandifoliola also recorded average total height of 5.50 ± 0.13 m and merchantable height 3.63 ± 0.09 m in pure stands, compared to total height of 5.04 ± 0.24 m and merchantable height of 3.52 ± 0.18 m in mixed stands. However, these values were not significantly different between the stands (P > 0.05). Basal area at breast height for K. grandifoliola grown in pure stands was 5.5 ± 0.3 m2/ha at age four, which was significantly higher than the basal area of 1.1 ± 0.4 m2/ha at breast height for K. grandifoliola in mixed stands. Also total volume per hectare was higher in pure stands (17.8 ± 0.9 m3/ha) than in mixed stands (3.4 ± 0.6 m3/ha). Consequently, K. grandifoliola accumulated more carbon in pure stands (10,126 ± 557.2 kg/ha) than in mixed stands (1,976 ± 335.1 kg/ha), but the mixture of the tree species, including K. grandifoliola, accumulated more carbon (11,929 ± 401.3 kg/ha) than the K. grandifoliola in pure stands though not statistically different. Overall, K. grandifoliola performed better in pure stands than in mixed stands. With regards to the tolerance to pest attacks on K. grandifoliola, it was more tolerant to pests’ attacks in mixed stands than in pure stands. There was no statistical difference in diameter growth between K. grandifoliola (9.15 ± 0.19 cm) and T. grandis (9.61 ± 0.26 cm) in pure stands. The values of total height, merchantable height and total volume for T. grandis were 8.22 ± 0.20 m, 5.38 ± 0.18 m and 22.5 ± 1.7 m3/ha respectively which differed significantly from 5.50 ± 0.13 m, 3.63 ± 0.09 m and 17.8 ± 0.9 m3/ha for K. grandifoliola for the same parameters (P < 0.05). However, there was no significant difference between the two species with respect to basal area per hectare (P = 0.189); K. grandifoliola grew to 5.5 ± 0.3 m2/ha and T. grandis grew to 4.8 ± 0.3 m2/ha. T. grandis in pure stands accumulated slightly more aboveground biomass than K. grandifoliola in pure stands after 4 years though not statistically different.

As they fulfil many ecological and social functions and services better than even-aged monocultures, heterogeneous pure and mixed-species stands are on the advance in Central Europe. Even so, knowledge of how different stands compare in terms of the quantity and quality of the produced wood remains limited, as forest research has been focused on pure stands in the past. Therefore, the still limited comparative studies on timber quality in mixed versus pure stands were reviewed. Further, approximately 100 studies on the morphology of mixed versus pure stands have been reviewed. As is known, the close connection between morphology and timber quality from many studies in pure stands as well as the morphological and structural properties of trees in mixed stands is used as proxies for their timber quality. The number of studies reporting a decrease or increase in timber strength and stiffness in complex stands compared with homogeneous stands was balanced. Knottiness is mostly higher in complex stands. Wood density behaves indifferently. Distortion, as indicated by eccentricity of crown, bending of stems, or irregularity of the tree-ring width, is generally higher in complex forests. This rather ambiguous pattern becomes clearer by typifying the findings depending on the species-specific morphological plasticity of the trees and the spatial conditions they are exposed to. When growing in strong lateral restriction in even-aged pure or mixed-species stands (type 1), trees follow a “keep abreast” strategy which results in high-quality timber especially in case of species with low plasticity. Trees in uneven-aged forests with vertically restricted growing space (type 2) often use a “sit-and-wait” strategy that may result in tapering stem shapes, wide and long crowns with low branch diameters, and high wood density. Distortion may be low in case of species with low morphological plasticity but increase with increasing shade tolerance and plasticity. Growth in widely spaced and heavily thinned pure and mixed stands (type 3) may let trees follow the “stabilisation” strategy. Because of their strong dominance, these trees develop tapering stem shapes, knots of big size and wide appearance along the stem axis, as well as lower wood density, especially in the case of conifers. In arrangements of types 1–3, the “transition” strategy may also emerge, which leads from the “sit-and-wait” stadium to the “keep abreast” strategy. It starts when trees strongly increase their height growth at the expense of the stem diameter growth. It results in slender stems, low knottiness, high wood density, and low distortion, with the result that the tree gets access to the upper canopy at the expense of lateral expansion of stem and crown. In fact, it is not primarily the species mixing that modifies the morphology, structure, and wood quality of the trees but the species-specific morphological plasticity and the structural heterogeneity of the stand. The latter is often higher in mixed than in pure stands and in uneven-aged than in even-aged stands. The more variable the stand structure, the wider the range of wood attributes. The discussion is focused on the relevance of the results for stand management and interdisciplinary research at the intersection of forest growth and yield science and wood science.

We examined the effects of different tillage practices on plough layer soil structure and organic carbon stabilization in black soil farmland with a long-term positioning platform. The wet-sieving method and infrared spectroscopy method were used to investigate the impacts of conventional tillage (CT), no-tillage (NT), sub-soiling tillage (ST), and moldboard plowing tillage (MP) on soil aggregates distribution and organic carbon characteristics in 0-40 cm soil layers. Compared to CT, both NT and ST treatments significantly increased the proportion of large macroaggregates (>2 mm) in the topsoil layer (0-20 cm)and that of small macroaggregates (0.25-2 mm) in the subsoil layer (20-40 cm) for NT, ST, and MP. NT, ST, and MP treatments resulted in higher mean weight dia-meter (MWD) and mean geometric diameter (GMD) of soil aggregates in both the topsoil and subsoil layers. NT treatment improved organic carbon contents in bulk soil and large macroaggregates in the topsoil layer, while ST and MP enhanced organic carbon contents in bulk soil and large macroaggregates in the subsoil layer. The contribution rate of small macroaggregates organic carbon content to the total was between 68.9% and 83.4%. Furthermore, the organic carbon chemical stabilization of soil body and aggregates increased in the topsoil and subsoil layers under NT treatment compared to others. The MWD had a positive correlation with the organic carbon content and chemical stability of soil body and small macroaggregates. These findings offered a theoretical basis for understanding the impacts of different tillage practices on the stability of soil aggregate and organic carbon in black soil region.

Facilitation, reduced competition or increased competition can arise in mixed stands and become essential to the performance of these stands when compared to pure stands. Facilitation and over-yielding are widely held to prevail on poor sites, whereas neutral interactions or competition, leading to under-yielding of mixed versus pure stands, can occur on fertile sites. While previous studies have focused on the spatial variation of mixing effects, we examine the temporal variation of facilitation and competition and its effect on growth. The study is based on tree ring measurement on cores from increment borings from 559 trees of Norway spruce (Picea abies [L.] Karst.), European beech (Fagus sylvatica [L.]) and sessile oak (Quercus petraea (Matt.) Liebl.) in southern Germany, half of which were in pure stands and half in adjacent mixed stands. Mean basal area growth indices were calculated from tree ring measurements for pure and mixed stands for every species and site. The temporal variation, with positive correlations between species-specific growth indices during periods of low growth and neutral or negative correlations during periods of high growth, is more distinct in mixed than in neighbouring pure stands. We provide evidence that years with low growth trigger over-yielding of trees in mixed as opposed to pure stands, while years with high growth lead to under-yielding. We discuss the relevance of the results in terms of advancing our understanding and modelling of mixed stands, extension of the stress gradient hypothesis, and the performance of mixed versus pure stands in the face of climate change.

Influence of forest tree species composition on bryophytic diversity in mixed and pure pine (Pinus sylvestris L.) and oak (Quercus petraea (Matt.) Liebl.) stands

Mixing increases drought exposure through a faster growth in beech, but not in oak

Mixtures of legumes and non-legumes are often characterized by higher grain and biomass yields compared to their pure stands. Complementarity between plant species is assumed to be the major driver behind this aboveground overyielding. Cultivar characteristics can affect mixture performance. Nevertheless, novel legume cultivars/genotypes are primarily bred and tested for pure stand purposes. However, well-performing genotypes in pure stands do not necessarily perform similarly well in mixtures. To fully understand mixed cropping systems, it is necessary to investigate their underlying spatiotemporal above- and belowground processes. Roots are of particular importance for the plant, as they acquire water and nutrients. Nonetheless, little is known about differences in root biomass and distribution between pure stands and mixtures. So far, the lack of a simple and time-efficient method has hampered the analysis of root species proportions in mixtures. In the present study, novel legume genotypes of arable land and grassland were sown as pure stands and mixtures with non-legumes. Two different field experiments were conducted at the experimental station ‘Reinshof’ of the Georg-August-University of Goettingen (Germany) to investigate the biomass, root distribution and overyielding potential of these pure and mixed stands. In the arable land experiment, eight genotypes of winter faba bean (Vicia faba L.) and one cultivar of winter wheat (Triticum aestivum L., cv. Genius) were sown in pure stands and in substitutive 50/50 mixtures. The intra- and interspecific variation of shoot and root biomass, the horizontal and vertical root distribution and the overyielding potential were investigated in all crop stands at full flowering of faba bean. Aboveground biomass of 1 m² was harvested and roots were sampled in May 2015 and May 2016. Root samples were taken on and between rows with a root auger down to 60 cm soil depth. Fourier transform infrared (FTIR) spectroscopy was used to quantify species-specific root biomasses in mixtures. The vertical root distribution was evaluated using the equation y = 1 - βd (Gale and Grigal 1987). To assess above- and belowground mixture overyielding, the relative yield total (RYT) was calculated for shoot and root biomass. The results showed that all FTIR quantification models performed well in the prediction of root species proportions. Roots of both species proliferated into the soil space between the rows and under the mixture partner’s row to a similar extent. In mixtures, faba bean and wheat on their own row produced higher root fractions in shallower soil layers than in pure stands, while simultaneously both species had more roots in deeper soil layers under the partner’s row than on their own row. Overyielding of faba bean/wheat mixtures was more pronounced for belowground biomass than for aboveground biomass. In mixtures, faba bean genotypes differed significantly in root biomass, root:shoot ratio, overyielding potential and vertical root distribution on wheat rows but not in shoot biomass. In the grassland experiment, the root biomass of eight genotypes of white clover (Trifolium repens L.) and one perennial ryegrass genotype (Lolium perenne L., Elp 060687) were investigated. Four different crop stands were established in May 2014: (i) unfertilized clover pure stand of each clover genotype, (ii) unfertilized ryegrass pure stand, (iii) N-fertilized ryegrass pure stand and (iv) unfertilized mixture of each clover genotype with ryegrass. Similar to the first experiment, root sampling was conducted from 0 to 60 cm soil depth in June 2015. Clover and ryegrass root proportion in mixtures was determined via FTIR spectroscopy. Belowground RYT was calculated for each mixture. The results showed that FTIR models demonstrated a satisfactory residual predictive deviation. In pure stands as well as in mixtures, clover produced significantly lower root biomasses than ryegrass. Nitrogen fertilization did not affect the root biomass of ryegrass. In pure stands, clover root biomass differed significantly between genotypes. Furthermore, root RYT was higher than one in all the eight clover/ryegrass mixtures but differed between the genotypes. This belowground overyielding was mainly caused by the high relative root biomass of ryegrass. The present study showed that FTIR spectroscopy is a suitable tool for the identification and quantification of root species in legume/non-legume mixtures. From the two experiments, it can be concluded that both faba bean/wheat and clover/ryegrass mixtures overyield with regard to root biomass. Root overyielding in legume/non-legume mixtures compared to the pure stand equivalents might lead to better resource utilization and enhanced aboveground yields of these systems. The fact that genotypes performed differently in pure and mixed stands shows the potential of legume breeding for mixture purposes. In both arable land (Vf5) and grassland (Tr6), one legume genotype was identified for further breeding in mixed cropping systems. The results of the present study suggest that investigations of root properties should be included in mixture breeding processes.