Ecosystem Controls on C & N Sequestration Following Afforestation of Agricultural Lands

In our project, we proposed to continue analysis of our available soil samples and data, and to develop new studies to answer the following objectives: Objective 1) Broaden field based studies of ecosystem C and N compartments to enhance current understanding of C and N sequestration and dynamics. Objective 2) Improve our understanding of mechanism controlling C and N stabilization and dynamics. Objective 3) Investigate the interrelated role of soil temperature and organism type and activity as controlling mechanism in SOC dynamics and sequestration

Ecosystem Controls on C & N Sequestration Following Afforestation of Agricultural Lands

In our project, we proposed to continue analysis of our available soil samples and data, and to develop new studies to answer the following objectives: Objective 1) Broaden field based studies of ecosystem C and N compartments to enhance current understanding of C and N sequestration and dynamics. Objective 2) Improve our understanding of mechanism controlling C and N stabilization and dynamics. Objective 3) Investigate the interrelated role of soil temperature and organism type and activity as controlling mechanism in SOC dynamics and sequestration

Selective preservation of pyrogenic carbon across soil organic matter fractions and its influence on calculations of carbon mean residence times

The long-standing perspective that recalcitrance of soil organic carbon (SOC) controls its stability and persistence has shifted to one in which physical inaccessibility of SOC to microorganisms plays a predominant role. This paradigm shift has been facilitated by analytical techniques that isolate SOC into physical fractions protected from decomposers by different mechanisms. The correlation between these fractions and SOC age has reinforced the emphasis of SOC inaccessibility. Pyrogenic C (PyC; also called charcoal or black carbon), which has been thermally altered by fire, is known to contain highly recalcitrant components that decompose very slowly and could represent an exception to this paradigm shift. We employed hydrogen pyrolysis to quantify the contribution of PyC to total SOC across soil fractions from three long-term agricultural experiments with land use conversions that caused reductions in SOC. We show that all soil fractions contain PyC and up to one-fifth of SOC in soil fractions considered to have low accessibility is comprised of PyC. Regardless of the soil fraction in which it was located, PyC was relatively unaffected by land use conversion compared to biogenic C (organic C not altered by fire), which suggests that selective preservation, rather than physical protection, is the dominant mechanism limiting PyC decomposition in these sites. We accounted for PyC in calculations of C mean residence times (MRTs) using differences in stable C isotope ratios between PyC and SOC. Though results varied by site and soil fraction, MRTs for biogenic C were generally shorter than for total SOC. Based on these results, PyC decomposition is controlled by a different mechanism than biogenic C, and this should be considered in studies of soil C dynamics. In addition, methods based on physical fractionation alone may place too great an emphasis on the role of inaccessibility for long-term SOC persistence

Optimising seed processing techniques to improve germination and sowability of native grasses for ecological restoration

© 2018 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands Grasslands across the globe are undergoing expansive degradation due to human impacts and climate change. If restoration of degraded native grassland is to be achieved at the scale now required, cost-effective means for seed-based establishment of grass species is crucial. However, grass seeds present numerous challenges associated with handling and germination performance that must be overcome to improve the efficiency of seeding. Previous research has demonstrated that complete removal of the palea and lemma (husk) maximises germination performance, hence we investigated the effects of complete husk removal on seed handling and germination of four temperate Australian grass species. Three techniques were tested to remove the husk – manual cleaning, flaming or acid digestion (the latter two followed by a manual cleaning step); these techniques were refined and adapted to the selected species, and germination responses were compared. The complete removal of the husk improved seed handling and sowability for all species. Germination was improved in Microlaena stipoides by 19% and in Rytidosperma geniculatum by 11%. Of the husk removal methods tested, flaming was detrimental to seed germination and fatal for one species (R. geniculatum). Compared to manual cleaning, sulphuric acid improved the overall efficacy of the cleaning procedure and increased germination speed (T50) in Austrostipa scabra, Chloris truncata and M. stipoides, and improved final germination in R. geniculatum by 13%. The seed processing methods developed and tested in the present study can be applied to grass species that present similar handling and germination performance impediments. These and other technological developments (seed coating and precision sowing) will facilitate more efficient grassland restoration at large scale