The role of the biological soil-root interface in seasonal variation of N and P recycling for Aspalathus linearis

Thesis (MSc)--Stellenbosch University, 2023.

ENGLISH ABSTRACT: Aspalathus linearis is found in the diverse Cape Floristic Region, known for its nutrient poor soil with a low pH and weather conditions that consists of dry, hot summers and cold, wet winters. Aspalathus linearis is well adapted to the soil in this region by producing cluster roots, forming symbiotic relationships with nitrogen fixing bacteria and by increasing the soil pH through OH- secretion in the roots. Few studies have investigated the seasonal variation in A. linearis physiology with regards to N and P acquisition. This study aims to determine the seasonal variation in N and P acquisition for A. linearis grown in two different soils and determine the biological activities in the soil associated with A. linearis. It is expected that an increase in N and P enzyme activity will be seen for soil with higher nutrient levels. Two soils were identified, one with higher P and C concentrations and a higher clay percentage. Nitrogen and P acquisition was determining using enzyme assays, including GS, NR, GDH-D, GDH- A, Phytase, APase, RNAse and Pi. Soil chemical and physical properties were investigated to determine the differences in the soil and microbial community diversity were investigated in the study. The differences in soil showed a great impact on soil enzyme activity on enzymes such as NR and APase, while having little effect on other soil enzymes. Seasonal growth caused a significant increase in bacterial activity and diversity for both soils identified and an increase in wetter season was found in microbial diversity. Soil conditions such as higher C and P did not show a consistent impact on plant enzyme activity. Enzymes such as GS, GDH-A, GDH-D and Pi were affected by soil conditions, however, seasons affected activity more than soil. Amino acid concentrations increased in winter, with soil in higher C and P having significantly lower concentrations than amino acid concentrations from all winter material measured. The study found that an increase in nutrients including C and P does not lead to an overall increase in N and P acquisition and that enzyme activity varied in dependency on soil conditions. Further studies should investigate the effect of different soil conditions on drought for A. linearis.

AFRIKAANSE OPSOMMING: Aspalathus linearis kom in die diverse Kaapse Floristiese Streek voor, bekend vir sy voedingsarm grond met 'n lae pH en weerstoestande wat bestaan uit droë, warm somers en koue, nat winters. A. linearis is goed aangepas by die grond in hierdie streek deur troswortels te produseer, simbiotiese verwantskappe met stikstofbindende bakterieë te vorm en deur die grond pH te verhoog deur OH- af te skeid deur die wortels. Min studies het al die seisoenale variasie in A. linearis fisiologie met betrekking tot N- en P-verkryging ondersoek. Hierdie studie het ten doel om die seisoenale variasie in N- en P-verkryging vir A. linearis wat in twee verskillende gronde gekweek word te bepaal en die biologiese aktiwiteite in die grond wat met A. linearis geassosieer word, te bepaal. Daar word verwag dat 'n toename in N- en P- ensiemaktiwiteit gesien sal word vir grond met hoër voedingstofvlakke. Twee gronde is geïdentifiseer, een met hoër P- en C-konsentrasies en 'n hoër kleipersentasie. Stikstof- en P-verkryging was bepalend met behulp van ensiemtoetse, insluitend GS, NR, GDH-D, GDH-A, Phytase, APase, RNAse en Pi. Grond chemiese en fisiese eienskappe is ondersoek om die verskille in die grond te bepaal en mikrobiese gemeenskap diversiteit was in die studie ondersoek. Die verskille in grond het 'n groot impak op grondensiemaktiwiteit op ensieme soos NR en APase getoon, terwyl dit min effek op ander grondensieme gehad het. Seisoenale groei het 'n beduidende toename in bakteriese aktiwiteit en diversiteit veroorsaak vir beide gronde wat geïdentifiseer is en 'n toename in natter seisoen was gevind in mikrobiese diversiteit. Grondtoestande soos hoër C en P het nie 'n konsekwente impak op plantensiemaktiwiteit getoon nie. Ensieme soos GS, GDH-A, GDH-D en Pi was deur grondtoestande beïnvloed, maar seisoene het aktiwiteit meer as grond beïnvloed. Aminosuurkonsentrasies het in die winter toegeneem, met grond in hoër C en P wat aansienlik laer konsentrasies gehad het as aminosuurkonsentrasies van alle wintermateriaal wat gemeet is. Die studie het bevind dat 'n toename in voedingstowwe insluitend C en P nie lei tot 'n algehele toename in N- en P-verkryging nie en dat ensiemaktiwiteit verskil in afhanklikheid van grondtoestande. Verdere studies behoort die effek van verskillende grondtoestande op droogte te ondersoek vir A. linearis.

Masters